Possible to apply effects to the sound during a phonecall (iPhone)?

So can I catch the s开发者_C百科ound input, and manipulate it before it "sends" to the phonemate?

Apple does not provide public APIs to interact with a phone call. As BoltClock mentioned in his comment, it may be possible to use private APIs for this, but Apple would not allow a program that uses private APIs to be sold on the app store.