docs: Add Realtime SIP document section

docs/src/content/docs/guides/voice-agents/transport.mdx

@@ -22,6 +22,7 @@ import historyUpdatedExample from '../../../../../../examples/docs/voice-agents/
 import updateHistoryExample from '../../../../../../examples/docs/voice-agents/updateHistory.ts?raw';
 import customWebRTCTransportExample from '../../../../../../examples/docs/voice-agents/customWebRTCTransport.ts?raw';
 import websocketSessionExample from '../../../../../../examples/docs/voice-agents/websocketSession.ts?raw';
+import sipTransportExample from '../../../../../../examples/docs/voice-agents/sipTransport.ts?raw';
 import transportEventsExample from '../../../../../../examples/docs/voice-agents/transportEvents.ts?raw';
 import thinClientExample from '../../../../../../examples/docs/voice-agents/thinClient.ts?raw';
 import cloudflareTransportExample from '../../../../../../examples/docs/extensions/cloudflare-basic.ts?raw';
@@ -47,6 +48,16 @@ building a phone agent with Twilio.
 
 Use any recording/playback library to handle the raw PCM16 audio bytes.
 
+### Connecting over SIP
+
+Bridge SIP calls from providers such as Twilio by using the `OpenAIRealtimeSIP` transport. The transport keeps the Realtime session synchronized with SIP events emitted by your telephony provider.
+
+1. Accept the incoming call by generating an initial session configuration with `OpenAIRealtimeSIP.buildInitialConfig()`. This ensures the SIP invitation and Realtime session share identical defaults.
+2. Attach a `RealtimeSession` that uses the `OpenAIRealtimeSIP` transport and connect with the `callId` issued by the provider webhook.
+3. Listen for session events to drive call analytics, transcripts, or escalation logic.
+
+<Code lang="typescript" code={sipTransportExample} />
+
 #### Cloudflare Workers (workerd) note
 
 Cloudflare Workers and other workerd runtimes cannot open outbound WebSockets using the global `WebSocket` constructor. Use the Cloudflare transport from the extensions package, which performs the `fetch()`-based upgrade internally.

examples/docs/voice-agents/sipTransport.ts

@@ -0,0 +1,57 @@
+import OpenAI from 'openai';
+import {
+  OpenAIRealtimeSIP,
+  RealtimeAgent,
+  RealtimeSession,
+  type RealtimeSessionOptions,
+} from '@openai/agents/realtime';
+
+const openai = new OpenAI({
+  apiKey: process.env.OPENAI_API_KEY!,
+  webhookSecret: process.env.OPENAI_WEBHOOK_SECRET!,
+});
+
+const agent = new RealtimeAgent({
+  name: 'Receptionist',
+  instructions:
+    'Welcome the caller, answer scheduling questions, and hand off if the caller requests a human.',
+});
+
+const sessionOptions: Partial<RealtimeSessionOptions> = {
+  model: 'gpt-realtime',
+  config: {
+    audio: {
+      input: {
+        turnDetection: { type: 'semantic_vad', interruptResponse: true },
+      },
+    },
+  },
+};
+
+export async function acceptIncomingCall(callId: string): Promise<void> {
+  const initialConfig = await OpenAIRealtimeSIP.buildInitialConfig(
+    agent,
+    sessionOptions,
+  );
+  await openai.realtime.calls.accept(callId, initialConfig);
+}
+
+export async function attachRealtimeSession(
+  callId: string,
+): Promise<RealtimeSession> {
+  const session = new RealtimeSession(agent, {
+    transport: new OpenAIRealtimeSIP(),
+    ...sessionOptions,
+  });
+
+  session.on('history_added', (item) => {
+    console.log('Realtime update:', item.type);
+  });
+
+  await session.connect({
+    apiKey: process.env.OPENAI_API_KEY!,
+    callId,
+  });
+
+  return session;
+}