This is a post from Android Developers about the Android 4.0 APIs.
http://developer.android.com/about/versions/android-4.0.html
If you scroll down there is a section about Voicemail Providers where it explains:
Because the APIs currently do not allow third-party apps to read all the voicemails from the system, the only third-party apps that should use the voicemail APIs are those that have voicemail to deliver to the user.
However, I assume if you are trying to receive voicemails from a third party and not from your service then this still may be possible. Check out this link about VoicemailContracts where I believe it says you need the permission ADD_VOICEMAIL in your manifest to use the actions you are using above.
http://developer.android.com/reference/android/provider/VoicemailContract.html
There are also samples that I did not get a chance to look at called Voicemail Provider Demo in your SDK. I hope this helps.