Does anyone know if it's possible to take a recorded audio file and play it over the iPhone radio during a call? I realize that it's possible to play it on the speaker so that the mic picks it up and includes it with the audio of the actual call, but what I'd really like to do is play the sound directly into the phone call (i.e. not over the speaker). I also realize that this is not possible using public Apple-approved APIs.

Thanks in advance.