Update docs on voice fallback plans

fern/voice-fallback-plan.mdx

@@ -10,9 +10,11 @@ slug: voice-fallback-plan
 
 ## Introduction
 
-By default, if an assistant's primary voice experiences any failure, Vapi will automatically attempt to use other available voices to continue the call. While this ensures call continuity, you might want more control over which specific voices are used as fallbacks.
+Voice fallback plans give you the ability to continue your call in the event that your primary voice fails. Your assistant will sequentially fallback to only the voices you configure within your plan, in the exact order you specify. 
 
-Fallback plans give you precise control over the fallback sequence. Your assistant will sequentially fallback to only the voices you configure within your plan, in the exact order you specify. 
+<Note>
+  Without a fallback plan, your call will end in the event that your primary voice fails.
+</Note>
 
 ## How It Works
 
@@ -22,10 +24,6 @@ When a voice failure occurs, Vapi will:
   - Switch to the first fallback voice in your plan
   - Continue through your specified list if subsequent failures occur
   - Terminate only if all voices in your plan have failed
-3. If no custom fallback plan is configured:
-  - Automatically switch to other available voices
-  - Continue attempting different voices
-  - Terminate only if all available voices have failed
 
 ## Configuration
 
@@ -54,20 +52,6 @@ Add the `fallbackPlan` property to your assistant's voice configuration, and spe
 }
 ```
 
-Although **not recommended**, you may choose to disable the default fallback behavior by providing an empty list of voices in your fallback plan:
-
-```json
-{
-  "voice": {
-    "provider": "openai",
-    "voiceId": "shimmer",
-    "fallbackPlan": {
-        "voices": []
-    }
-  }
-}
-```
-
 ## Best practices
 
 - Use <b>different providers</b> for your fallback voices to protect against provider-wide outages.