First to say, I don't have an Android phone yet, I'm still thinking about buying one to learn mobile programming. I also have a question about one idea which comes into my mind when thinking about mobile development.
Let's say I'd like to apply some kind of audio transformation for incoming call, more complicated than volume up/down :). Is it possible to intercept incoming audio as binary data, do some transformations on it, and send it to the speaker? And, the other way: is it possible to intercept voice from a microphone as binary data, do some transformations, and sent it through GSM?
My idea is to write an encryption software, which would encrypt your voice when you speak, send encrypted data stream over the network, then the second (Android) phone will decrypt it, and the other guy will hear my voice already decrypted.
Is it possible to do with current state of Android? If not, maybe someone has the knowledge about different systems (Symbian?) which allow doing such a thing?