The Phone app sends this intent when a user opts to respond-via-message during an incoming call. By default, the device's default SMS app consumes this message and sends a text message to the caller. A third party app can also provide this functionality by consuming this Intent with a Android.App.Service and sending the message using its own messaging system.

The intent contains a URI (available from Android.Content.Intent.Data) describing the recipient, using either the sms:, smsto:, mms:, or mmsto: URI schema. Each of these URI schema carry the recipient information the same way: the path part of the URI contains the recipient's phone number or a comma-separated set of phone numbers if there are multiple recipients. For example, smsto:2065551234.

The intent may also contain extras for the message text (in Android.Content.Intent.ExtraText) and a message subject (in Android.Content.Intent.ExtraSubject).

Note: The intent-filter that consumes this Intent needs to be in a Android.App.Service that requires the permission NoType:android/Manifest$permission;Href=../../../reference/android/Manifest.permission.html#SEND_RESPOND_VIA_MESSAGE.

For example, the service that receives this intent can be declared in the manifest file with an intent filter like this:

 <!-- Service that delivers SMS messages received from the phone "quick response" -->
 <service android:name=".HeadlessSmsSendService"
          android:permission="android.permission.SEND_RESPOND_VIA_MESSAGE"
          android:exported="true" >
   <intent-filter>
     <action android:name="android.intent.action.RESPOND_VIA_MESSAGE" />
     <category android:name="android.intent.category.DEFAULT" />
     <data android:scheme="sms" />
     <data android:scheme="smsto" />
     <data android:scheme="mms" />
     <data android:scheme="mmsto" />
   </intent-filter>
 </service>

Output: nothing.

[Android Documentation]