You need to look at android.media
Android.media[
^]
android.media gives you all the option to record from.
Skeleton code
final MediaRecorder Callrecorder = new MediaRecorder();
Callrecorder.setAudioSource(MediaRecorder.AudioSource.VOICE_CALL);
Callrecorder.setOutputFormat(MediaRecorder.OutputFormat.THREE_GPP);
Callrecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AMR_NB);
Callrecorder.setOutputFile(recordPath);
Callrecorder.prepare();
Callrecorder.start();
... do something else
Callrecorder.stop();
This should help you with the idea.
/Darren