thanks. i'll look into that.
ATM cells are really small (about 48 bytes) but have a Virtual Channel and Virtual Path indicator in the header. But maybe going that low isn't all that necessary up front.
and prank calls are just the 'public face' of this idea. you can pass out a program with instructions on how to spoof a phone number, but those that know will be able to use it for alot more (for example, tunneling sensitive information through the audio signal of a phone conversation that is inserted and extracted using phase vocoding synthesis techniques, which then can be routed through various phones to avoid tracing). and of course, there will be little instruction (ie none) shipped with the app.