diff --git a/enterprise/app/controllers/twilio/voice_controller.rb b/enterprise/app/controllers/twilio/voice_controller.rb
index 66fef9583..52ec2637b 100644
--- a/enterprise/app/controllers/twilio/voice_controller.rb
+++ b/enterprise/app/controllers/twilio/voice_controller.rb
@@ -107,8 +107,8 @@ class Twilio::VoiceController < ApplicationController
     when 'inbound'
       Voice::InboundCallBuilder.perform!(
         inbox: inbox,
-        from_number: twilio_from,
-        call_sid: twilio_call_sid
+        call_sid: twilio_call_sid,
+        caller: { source_ids: [twilio_from], contact_attributes: { name: twilio_from, phone_number: twilio_from } }
       )
     when 'outbound-api', 'outbound-dial'
       sync_outbound_leg(call_sid: twilio_call_sid, direction: twilio_direction)
diff --git a/enterprise/app/services/voice/inbound_call_builder.rb b/enterprise/app/services/voice/inbound_call_builder.rb
index eef70e76b..c928da43f 100644
--- a/enterprise/app/services/voice/inbound_call_builder.rb
+++ b/enterprise/app/services/voice/inbound_call_builder.rb
@@ -1,17 +1,19 @@
 class Voice::InboundCallBuilder
-  attr_reader :inbox, :from_number, :call_sid, :provider, :extra_meta
+  attr_reader :inbox, :call_sid, :provider, :extra_meta, :source_ids, :contact_attributes
 
-  def self.perform!(inbox:, from_number:, call_sid:, provider: :twilio, extra_meta: {})
-    new(inbox: inbox, from_number: from_number, call_sid: call_sid,
-        provider: provider, extra_meta: extra_meta).perform!
+  # `caller` carries the contact identity: { source_ids:, contact_attributes: }. Twilio passes
+  # its single +phone source_id; WhatsApp passes the message-path phone/user_id/parent_user_id set.
+  def self.perform!(inbox:, call_sid:, caller:, provider: :twilio, extra_meta: {})
+    new(inbox: inbox, call_sid: call_sid, caller: caller, provider: provider, extra_meta: extra_meta).perform!
   end
 
-  def initialize(inbox:, from_number:, call_sid:, provider: :twilio, extra_meta: {})
+  def initialize(inbox:, call_sid:, caller:, provider: :twilio, extra_meta: {})
     @inbox = inbox
-    @from_number = from_number
     @call_sid = call_sid
     @provider = provider.to_sym
     @extra_meta = extra_meta || {}
+    @source_ids = Array(caller[:source_ids]).compact_blank
+    @contact_attributes = caller[:contact_attributes] || {}
   end
 
   def perform!
@@ -43,46 +45,17 @@ class Voice::InboundCallBuilder
         .find_by(provider: provider, provider_call_id: call_sid)
   end
 
-  # Always look up by (inbox, source_id) first — that pair has a UNIQUE index, so
-  # creating with a colliding source_id under a different contact would raise
-  # RecordNotUnique. Reuse the existing ContactInbox (and its contact) when found.
-  # A concurrent message webhook for the same wa_id can win the (inbox_id, source_id)
-  # race; rescue and re-find so the call path doesn't drop the connect.
+  # Resolve the contact/ContactInbox the same way inbound messages do — match across every
+  # candidate source_id (phone + BSUID aliases) so a call reuses the existing thread, creating
+  # one keyed on the first (phone, else BSUID) only when none exists. Shared with messaging via
+  # ContactInboxSourceIdResolver, which also rescues the concurrent-webhook create race.
   def ensure_contact_inbox!
-    sid = source_id_for_provider
-    existing = inbox.contact_inboxes.find_by(source_id: sid)
-    return existing if existing
-
-    ContactInbox.create!(contact: ensure_contact!, inbox: inbox, source_id: sid)
-  rescue ActiveRecord::RecordNotUnique
-    inbox.contact_inboxes.find_by!(source_id: sid)
+    ContactInboxSourceIdResolver.new(
+      inbox: inbox, source_ids: source_ids, contact_attributes: contact_attributes
+    ).perform
   end
 
-  def ensure_contact!
-    contact = account.contacts.find_or_create_by!(phone_number: from_number) do |record|
-      record.name = contact_name.presence || from_number
-    end
-    contact.update!(name: contact_name) if contact_name.present? && contact.name == from_number
-    contact
-  end
-
-  # WhatsApp inbound calls carry the caller's profile name in extra_meta; Twilio
-  # calls don't, so contact naming falls back to the phone number.
-  def contact_name
-    extra_meta['contact_name'].presence
-  end
-
-  # WhatsApp ContactInbox.source_id must be digits-only (the wa_id); Twilio accepts the +.
-  # Run BR/AR-style wa_id normalization (same path messaging uses) so an inbound call
-  # finds the existing ContactInbox instead of forking a new contact/conversation.
-  def source_id_for_provider
-    return from_number unless provider == :whatsapp
-
-    digits = from_number.to_s.delete_prefix('+')
-    Whatsapp::PhoneNumberNormalizationService.new(inbox).normalize_and_find_contact_by_provider(digits, :cloud)
-  end
-
-  # Mirror incoming-message routing: reuse the open conversation (or the last one when locked), else create new.
+  # Mirror Whatsapp::IncomingMessageBaseService#set_conversation: reuse this row's open conversation (or last when locked), else create.
   def resolve_conversation!(contact, contact_inbox)
     reusable = if inbox.lock_to_single_conversation
                  contact_inbox.conversations.last
diff --git a/enterprise/app/services/whatsapp/inbound_call_identity_builder.rb b/enterprise/app/services/whatsapp/inbound_call_identity_builder.rb
new file mode 100644
index 000000000..590a1f923
--- /dev/null
+++ b/enterprise/app/services/whatsapp/inbound_call_identity_builder.rb
@@ -0,0 +1,48 @@
+class Whatsapp::InboundCallIdentityBuilder
+  pattr_initialize [:inbox!, :params!]
+
+  # Build the message path's source_id set (phone wa_id -> user_id -> parent_user_id) plus
+  # contact attributes, so the resolver lands a call on the same ContactInbox a message would.
+  # BSUIDs ride in from_user_id/from_parent_user_id (or the contact's user_id/parent_user_id),
+  # never in `from` (the phone wa_id).
+  def perform(payload)
+    contact = caller_contact(payload)
+    phone = contact[:wa_id].presence || payload[:from].presence
+    source_ids = [
+      phone_source_id(phone),
+      payload[:from_user_id].presence || contact[:user_id].presence,
+      payload[:from_parent_user_id].presence || contact[:parent_user_id].presence
+    ].compact_blank.uniq
+    { source_ids: source_ids, contact_attributes: contact_attributes(contact, phone, source_ids.first) }
+  end
+
+  private
+
+  # Normalize the wa_id the same way messaging does so a call matches its stored source_id.
+  def phone_source_id(phone)
+    return unless phone.to_s.match?(/\A\d{1,15}\z/)
+
+    Whatsapp::PhoneNumberNormalizationService.new(inbox).normalize_and_find_contact_by_provider(phone.to_s, :cloud)
+  end
+
+  def contact_attributes(contact, phone, source_identifier)
+    name = contact.dig(:profile, :name).presence || source_identifier
+    return { name: name } unless phone.to_s.match?(/\A\d{1,15}\z/)
+
+    formatted = "+#{phone}"
+    { name: name == phone ? formatted : name, phone_number: formatted }
+  end
+
+  # Match the contacts entry to THIS caller so batched payloads don't borrow another's identity.
+  def caller_contact(payload)
+    Array(params[:contacts]).map(&:with_indifferent_access).find do |c|
+      identifier_match?(c[:wa_id], payload[:from]) ||
+        identifier_match?(c[:user_id], payload[:from_user_id]) ||
+        identifier_match?(c[:parent_user_id], payload[:from_parent_user_id])
+    end || {}.with_indifferent_access
+  end
+
+  def identifier_match?(left, right)
+    left.present? && right.present? && left.to_s == right.to_s
+  end
+end
diff --git a/enterprise/app/services/whatsapp/incoming_call_service.rb b/enterprise/app/services/whatsapp/incoming_call_service.rb
index 11b35d95a..ea08c8415 100644
--- a/enterprise/app/services/whatsapp/incoming_call_service.rb
+++ b/enterprise/app/services/whatsapp/incoming_call_service.rb
@@ -95,28 +95,21 @@ class Whatsapp::IncomingCallService
   # commit) already terminal, never `ringing` — agents aren't rung for a dead call.
   def build_inbound_call(payload, sdp_offer)
     ActiveRecord::Base.transaction do
-      call = Voice::InboundCallBuilder.perform!(inbox: inbox, from_number: "+#{payload[:from]}", call_sid: payload[:id],
-                                                provider: :whatsapp, extra_meta: inbound_extra_meta(payload, sdp_offer))
+      identity = Whatsapp::InboundCallIdentityBuilder.new(inbox: inbox, params: params).perform(payload)
+      extra_meta = { 'sdp_offer' => sdp_offer, 'ice_servers' => Call.default_ice_servers }
+      call = Voice::InboundCallBuilder.perform!(inbox: inbox, call_sid: payload[:id],
+                                                provider: :whatsapp, extra_meta: extra_meta, caller: identity)
+      sync_caller_identifiers(call, identity)
       tombstone = consume_terminate_tombstone(payload[:id])
       finalize_terminate(call, tombstone['duration'], tombstone['terminate_reason']) if tombstone
       call
     end
   end
 
-  def inbound_extra_meta(payload, sdp_offer)
-    extra_meta = { 'sdp_offer' => sdp_offer, 'ice_servers' => Call.default_ice_servers }
-    name = caller_profile_name(payload)
-    extra_meta['contact_name'] = name if name.present?
-    extra_meta
-  end
-
-  # Match strictly on wa_id (== calls[].from): in a batched payload missing this
-  # call's contact entry, borrowing another caller's name would corrupt this
-  # contact, so fall back to the phone number (nil here) instead of contacts.first.
-  def caller_profile_name(payload)
-    contacts = Array(params[:contacts]).map(&:with_indifferent_access)
-    match = contacts.find { |c| c[:wa_id].to_s == payload[:from].to_s }
-    match&.dig(:profile, :name).presence
+  # Backfill every caller alias (the builder only stores the first) so a later event keyed on any one lands on this thread.
+  def sync_caller_identifiers(call, identity)
+    Whatsapp::IdentifierSyncService.new(contact_inbox: call.conversation.contact_inbox, contact: call.contact)
+                                   .perform(source_ids: identity[:source_ids], phone_number: identity.dig(:contact_attributes, :phone_number))
   end
 
   # `connect` is the WebRTC tunnel-ready signal, not the pickup signal. Apply
diff --git a/spec/enterprise/controllers/twilio/voice_controller_spec.rb b/spec/enterprise/controllers/twilio/voice_controller_spec.rb
index 79fdd67a8..0f537af20 100644
--- a/spec/enterprise/controllers/twilio/voice_controller_spec.rb
+++ b/spec/enterprise/controllers/twilio/voice_controller_spec.rb
@@ -33,8 +33,8 @@ RSpec.describe 'Twilio::VoiceController', type: :request do
 
       expect(Voice::InboundCallBuilder).to receive(:perform!).with(
         inbox: inbox,
-        from_number: from_number,
-        call_sid: call_sid
+        call_sid: call_sid,
+        caller: { source_ids: [from_number], contact_attributes: { name: from_number, phone_number: from_number } }
       ).and_return(call)
 
       post "/twilio/voice/call/#{digits}", params: {
diff --git a/spec/enterprise/services/voice/inbound_call_builder_spec.rb b/spec/enterprise/services/voice/inbound_call_builder_spec.rb
index e36c9a1b7..c8c6b978e 100644
--- a/spec/enterprise/services/voice/inbound_call_builder_spec.rb
+++ b/spec/enterprise/services/voice/inbound_call_builder_spec.rb
@@ -17,8 +17,8 @@ RSpec.describe Voice::InboundCallBuilder do
   def perform_builder
     described_class.perform!(
       inbox: inbox,
-      from_number: from_number,
-      call_sid: call_sid
+      call_sid: call_sid,
+      caller: { source_ids: [from_number], contact_attributes: { name: from_number, phone_number: from_number } }
     )
   end
 
@@ -100,26 +100,29 @@ RSpec.describe Voice::InboundCallBuilder do
     end
   end
 
-  context 'when the WhatsApp wa_id needs Brazil normalization to match an existing ContactInbox' do
+  context 'when a WhatsApp call shares a BSUID with an existing ContactInbox' do
     let(:whatsapp_channel) do
       create(:channel_whatsapp, account: account, provider: 'whatsapp_cloud',
                                 provider_config: { 'phone_number_id' => '123', 'source' => 'embedded_signup', 'calling_enabled' => true },
                                 validate_provider_config: false, sync_templates: false)
     end
     let(:whatsapp_inbox) { whatsapp_channel.inbox }
-    let!(:stored_contact) { create(:contact, account: account, phone_number: '+5541988887777') }
+    let!(:stored_contact) { create(:contact, account: account) }
     let!(:stored_contact_inbox) do
-      create(:contact_inbox, contact: stored_contact, inbox: whatsapp_inbox, source_id: '5541988887777')
+      create(:contact_inbox, contact: stored_contact, inbox: whatsapp_inbox, source_id: 'IN.2081978709342942')
     end
 
     before { account.enable_features!('channel_voice') }
 
-    it 'reuses the contact via normalized wa_id rather than forking a new ContactInbox' do
+    # Closes the gap: the contact was keyed by BSUID, but the call also carries a phone.
+    # Matching across every source_id reuses the contact instead of forking on the phone.
+    it 'reuses the contact by matching any source_id, not just the first' do
       call = described_class.perform!(
         inbox: whatsapp_inbox,
-        from_number: '+554188887777',
-        call_sid: 'wacall_br_1',
-        provider: :whatsapp
+        call_sid: 'wacall_bsuid_1',
+        provider: :whatsapp,
+        caller: { source_ids: ['5541988887777', 'IN.2081978709342942'],
+                  contact_attributes: { name: 'Ada Lovelace', phone_number: '+5541988887777' } }
       )
 
       expect(call.contact).to eq(stored_contact)
diff --git a/spec/enterprise/services/whatsapp/incoming_call_service_spec.rb b/spec/enterprise/services/whatsapp/incoming_call_service_spec.rb
index a3c5246d2..cf031f1ca 100644
--- a/spec/enterprise/services/whatsapp/incoming_call_service_spec.rb
+++ b/spec/enterprise/services/whatsapp/incoming_call_service_spec.rb
@@ -74,6 +74,120 @@ describe Whatsapp::IncomingCallService do
     end
   end
 
+  describe 'inbound connect from a username (BSUID) caller' do
+    let(:sdp_offer) { "v=0\r\n...sdp..." }
+    let(:bsuid) { 'IN.2081978709342942' }
+    let!(:agent) { create(:user, account: account) }
+
+    before { create(:inbox_member, inbox: inbox, user: agent) }
+
+    it 'keys a phone caller by the phone (matching messaging) even when a BSUID is also present' do
+      allow(ActionCable.server).to receive(:broadcast)
+
+      params = {
+        calls: [{ id: provider_call_id, from: from_number, from_user_id: bsuid, event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ wa_id: from_number, user_id: bsuid, profile: { name: 'Ada Lovelace' } }]
+      }
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1).and change(Conversation, :count).by(1)
+
+      contact_inbox = Call.last.conversation.contact_inbox
+      expect(contact_inbox.source_id).to eq(from_number)
+      expect(contact_inbox.contact.name).to eq('Ada Lovelace')
+    end
+
+    it 'keys a username-only caller by the BSUID when no phone `from` is present' do
+      allow(ActionCable.server).to receive(:broadcast)
+
+      params = {
+        calls: [{ id: provider_call_id, from_user_id: bsuid, event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ user_id: bsuid, profile: { name: 'Ada Lovelace' } }]
+      }
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1)
+
+      contact_inbox = Call.last.conversation.contact_inbox
+      expect(contact_inbox.source_id).to eq(bsuid)
+      expect(contact_inbox.contact.name).to eq('Ada Lovelace')
+    end
+
+    it 'reuses the phone-keyed ContactInbox messaging created for a phone caller and backfills the BSUID alias' do
+      allow(ActionCable.server).to receive(:broadcast)
+      contact = create(:contact, account: account)
+      existing = create(:contact_inbox, inbox: inbox, contact: contact, source_id: from_number)
+
+      params = {
+        calls: [{ id: provider_call_id, from: from_number, from_user_id: bsuid, event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ wa_id: from_number, user_id: bsuid }]
+      }
+      # The conversation reuses the existing phone thread; the BSUID alias is backfilled onto the same contact.
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1).and change(ContactInbox, :count).by(1)
+
+      expect(Call.last.contact).to eq(contact)
+      expect(Call.last.conversation.contact_inbox).to eq(existing)
+      expect(inbox.contact_inboxes.find_by(source_id: bsuid).contact).to eq(contact)
+    end
+
+    it 'reuses a phone ContactInbox via the same wa_id normalization messaging uses' do
+      allow(ActionCable.server).to receive(:broadcast)
+      contact = create(:contact, account: account, phone_number: '+5541988887777')
+      existing = create(:contact_inbox, inbox: inbox, contact: contact, source_id: '5541988887777')
+
+      params = {
+        calls: [{ id: provider_call_id, from: '554188887777', event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ wa_id: '554188887777' }]
+      }
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1).and not_change(ContactInbox, :count)
+
+      expect(Call.last.conversation.contact_inbox).to eq(existing)
+    end
+
+    it 'reuses the BSUID-keyed ContactInbox messaging created for a username-only caller' do
+      allow(ActionCable.server).to receive(:broadcast)
+      contact = create(:contact, account: account)
+      existing = create(:contact_inbox, inbox: inbox, contact: contact, source_id: bsuid)
+
+      params = {
+        calls: [{ id: provider_call_id, from_user_id: bsuid, event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ user_id: bsuid }]
+      }
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1).and not_change(ContactInbox, :count)
+
+      expect(Call.last.contact).to eq(contact)
+      expect(Call.last.conversation.contact_inbox).to eq(existing)
+    end
+
+    # The gap: messaging created the contact username-only (BSUID-keyed), and the call now
+    # also exposes a phone. Matching across every source_id reuses the BSUID thread instead
+    # of forking a new phone-keyed contact.
+    it 'reuses a BSUID-keyed ContactInbox even when the call also carries a phone and backfills the phone alias' do
+      allow(ActionCable.server).to receive(:broadcast)
+      contact = create(:contact, account: account)
+      existing = create(:contact_inbox, inbox: inbox, contact: contact, source_id: bsuid)
+
+      params = {
+        calls: [{ id: provider_call_id, from: from_number, from_user_id: bsuid, event: 'connect',
+                  session: { sdp: sdp_offer, sdp_type: 'offer' } }],
+        contacts: [{ wa_id: from_number, user_id: bsuid }]
+      }
+      # The conversation reuses the existing BSUID thread; the phone alias is backfilled onto the same contact.
+      expect { described_class.new(inbox: inbox, params: params).perform }
+        .to change(Call, :count).by(1).and change(ContactInbox, :count).by(1)
+
+      expect(Call.last.contact).to eq(contact)
+      expect(Call.last.conversation.contact_inbox).to eq(existing)
+      expect(inbox.contact_inboxes.find_by(source_id: from_number).contact).to eq(contact)
+    end
+  end
+
   describe 'outbound connect (existing call)' do
     let!(:call) do
       conversation = create(:conversation, account: account, inbox: inbox)