why can't sound app record incoming phone conversation?

[mlevin77]

With a Verizon XV6700, I notice that the default sound recording application (Notes, which starts up when you hit the recorder button on the left of the phone) can record both sides of a phone conversation. But 3rd party apps (like Resco Sound Recorder, which I like because it makes MP3s on the fly) don't - they only record what I say, not what the other person says. Anyone know why?? Why can't other recording apps record both sides of the phone calls?

Mike