Android FCM + ConnectionService for AI Inbound Calls (2026)

Android does not have a separate VoIP push channel. You use FCM with high-priority on a data message, and you have a few seconds to show an incoming-call UI through the Telecom framework — or Android deprioritizes your next push.

Background

Firebase Cloud Messaging is the universal push channel on Android. For AI voice agents in 2026, the recipe is: send a high-priority data message, receive it in a service even from Doze, and immediately register an incoming call with the Telecom framework's CallsManager (or legacy ConnectionService for older devices). If you fail to show a UI, FCM will quietly throttle your next high-priority delivery — Google's quota system penalizes apps that abuse the priority lane.

The good news: with Core-Telecom CallsManager (Jetpack, alpha 2023, stable across 2024–2026), the boilerplate is now manageable. The bad news: every OEM (Samsung, Xiaomi, OPPO, Huawei) layers extra battery-optimization on top of stock Android, and you must convince users to whitelist your app or they will miss calls.

Architecture

```mermaid flowchart LR Backend[Voice Agent Backend] -- HTTP v1 API --> FCM[(Firebase FCM)] FCM -- high-priority data --> Device[Android Device] Device -- onMessageReceived --> Service[Foreground Service] Service -- addCall --> CallsManager[Core-Telecom CallsManager] CallsManager -- CallControlScope --> WebRTC[WebRTC PeerConnection] WebRTC -- SRTP --> Gateway[Pion Go gateway 1.23] ```

CallSphere implementation

The Android client across CallSphere's six verticals (real estate, healthcare, behavioral health, legal, salon, insurance) follows the same pattern:

• Real Estate (OneRoof) — High-priority FCM wakes the app, CallsManager surfaces the incoming UI, WebRTC peers the Pion Go gateway 1.23. NATS routes to the 6-container pod (CRM, MLS, calendar, SMS, audit, transcript). See /industries/real-estate.
• Healthcare — Same FCM + Telecom + WebRTC stack with HIPAA-safe opaque IDs. See /industries/healthcare.
• /demo browser path — Skip FCM entirely; runs in Chrome. See /demo.

37 agents · 90+ tools · 115+ DB tables · 6 verticals · HIPAA + SOC 2 · $149/$499/$1499 · 14-day /trial · 22% affiliate at /affiliate.

Build steps with code

```kotlin class VoiceMessagingService : FirebaseMessagingService() { override fun onMessageReceived(message: RemoteMessage) { val callId = message.data["call_id"] ?: return val from = message.data["from"] ?: "AI Agent"

// Start a foreground service so we have time to attach to Telecom
val intent = Intent(this, IncomingCallService::class.java).apply {
  putExtra("call_id", callId); putExtra("from", from)
}
ContextCompat.startForegroundService(this, intent)

} }

class IncomingCallService : Service() { override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int { startForeground(NOTIF_ID, buildPlaceholderNotification(), ServiceInfo.FOREGROUND_SERVICE_TYPE_PHONE_CALL)

val callsManager = CallsManager(this)
val attrs = CallAttributesCompat(
  displayName = intent?.getStringExtra("from") ?: "AI Agent",
  address = Uri.parse("voice:agent"),
  direction = CallAttributesCompat.DIRECTION_INCOMING,
  callType = CallAttributesCompat.CALL_TYPE_AUDIO_CALL,
)
CoroutineScope(Dispatchers.Main).launch {
  callsManager.addCall(attrs,
    onAnswer = { startWebRTC() },
    onDisconnect = { stopSelf() })
}
return START_NOT_STICKY

} } ```

```xml