added docs for sms chat

fern/chat/sms-chat.mdx

@@ -0,0 +1,126 @@
+---
+title: SMS chat
+subtitle: Enable text-based conversations with assistants via SMS messaging
+slug: chat/sms-chat
+---
+
+## Overview
+
+Let customers chat with your Vapi assistants through SMS text messages. Perfect for businesses that want to provide AI support through familiar messaging channels.
+
+**What You'll Enable:**
+* Text-based conversations through SMS
+* Automatic session management for each customer
+* Context-aware responses across message exchanges
+
+<Warning>
+SMS chat requires a **10DLC-approved Twilio number**. Only customers can initiate conversations - assistants cannot send the first message.
+</Warning>
+
+## Prerequisites
+
+* A [Vapi account](https://dashboard.vapi.ai/) with an existing assistant
+* A **10DLC-approved Twilio phone number** (required for assistant responses)
+* Basic understanding of [phone number management](/phone-numbers)
+
+---
+
+## Setup Steps
+
+<Steps>
+  <Step title="Import your 10DLC Twilio number">
+    Bring your approved Twilio number into Vapi so we can manage SMS messaging.
+
+    <Note>
+    SMS is **enabled by default** when importing Twilio numbers.
+    </Note>
+
+    See: [Import number from Twilio](/phone-numbers/import-twilio) and [Inbound SMS setup](/phone-numbers/inbound-sms)
+  </Step>
+  <Step title="Attach the number to an assistant">
+    Assign the assistant that will handle SMS conversations for this number.
+
+    When customers text your number, they'll automatically start a chat session with this assistant.
+  </Step>
+  <Step title="Test the integration">
+    Send a text message to your phone number to verify the assistant responds correctly.
+  </Step>
+</Steps>
+
+<Tip>
+View all SMS conversations in the [Session Logs](https://dashboard.vapi.ai/logs/session) page of your dashboard. Each SMS conversation creates a session where you can see the full message history and conversation flow.
+</Tip>
+
+---
+
+## How It Works
+
+When a customer texts your number:
+
+1. **Session Creation**: Vapi automatically creates a chat session for the customer
+2. **Context Management**: All messages maintain conversation context within the session
+3. **Response Delivery**: Assistant responses are sent back as SMS messages
+4. **Session Expiry**: Sessions expire after 24 hours of inactivity, then create fresh sessions for new conversations
+
+```mermaid
+sequenceDiagram
+    participant Customer
+    participant Twilio
+    participant Vapi
+    participant Assistant
+
+    Customer->>Twilio: "Hi, I need help"
+    Twilio->>Vapi: SMS webhook
+    Vapi->>Vapi: Create/find session
+    Vapi->>Assistant: Process message
+    Assistant->>Vapi: Generate response
+    Vapi->>Twilio: Send SMS response
+    Twilio->>Customer: "Hello! How can I help?"
+```
+
+---
+
+## Session Management
+
+SMS conversations use automatic session management:
+
+<Tabs>
+  <Tab title="Automatic Behavior">
+    * **New customers**: Get a fresh session on first text
+    * **Returning customers**: Continue existing session if under 24 hours
+    * **Session expiry**: After 24 hours, new session created automatically
+    * **Context preservation**: Full conversation history maintained within session
+  </Tab>
+  <Tab title="Manual Management">
+    You cannot manually manage SMS sessions - they're handled automatically by Vapi's SMS infrastructure.
+
+    For programmatic chat with manual session control, use the [Chat API](/chat/quickstart) directly.
+  </Tab>
+</Tabs>
+
+---
+
+## Limitations
+
+<Note>
+**Current SMS chat limitations:**
+- **10DLC requirement**: Only 10DLC-approved Twilio numbers support assistant responses
+- **Customer-initiated**: Assistants cannot send the first message to customers
+- **Query tool**: Knowledge-base searches are not supported (same as Chat API)
+- **Twilio only**: Other SMS providers are not currently supported
+</Note>
+
+---
+
+## Next Steps
+
+Enhance your SMS chat implementation:
+
+* **[Chat API](/chat/quickstart)** - Understand the underlying chat technology
+* **[Session management](/chat/session-management)** - Learn how sessions work in detail
+* **[Phone number management](/phone-numbers)** - Configure advanced telephony features
+* **[Assistant configuration](/assistants/quickstart)** - Optimize your assistant for text conversations
+
+<Tip>
+For the best SMS experience, configure your assistant with concise responses and clear conversation flows. SMS users expect quick, direct answers.
+</Tip>

fern/docs.yml

@@ -436,6 +436,9 @@ navigation:
           - page: Session management
             path: chat/session-management.mdx
             icon: fa-light fa-layer-group
+          - page: SMS chat
+            path: chat/sms-chat.mdx
+            icon: fa-light fa-comment-sms
           - page: Web widget
             path: chat/web-widget.mdx
             icon: fa-light fa-window-maximize

fern/phone-numbers/inbound-sms.mdx

@@ -71,3 +71,11 @@ Update your number to set `smsEnabled: true` if it was previously disabled.
 
 For full endpoint details, see the [OpenAPI reference](/api-reference/openapi).
 
+## Next steps
+
+Now that you have inbound SMS enabled:
+
+* **[SMS chat](/chat/sms-chat)** - Learn how customers can have full conversations with your assistants via SMS
+* **[Session management](/chat/session-management)** - Understand how SMS conversations maintain context automatically
+* **[Chat quickstart](/chat/quickstart)** - Explore the underlying chat technology powering SMS interactions
+