What is the difference between an intent filter declaration in action and a receiver?

I want my application to be registered by the phone call handler through the "Full action using ..." dialog. I found this to work if I use the following syntax in my manifest:

   <activity android:name="my.class">
       <intent-filter>
          <action android:name="android.intent.action.CALL_PRIVILEGED" />
          <category android:name="android.intent.category.DEFAULT" />
          <data android:scheme="tel" />
       </intent-filter>
   </activity>

but if I register it as a broadcast receiver, my application will not appear in the "Complete action using ..." dialog box.

   <receiver android:name="my.class">
       <intent-filter>
          <action android:name="android.intent.action.CALL_PRIVILEGED" />
          <category android:name="android.intent.category.DEFAULT" />
          <data android:scheme="tel" />
       </intent-filter>
   </receiver>

What is the difference between the two separately from the type of class that will be called after the Intent matches the filter?