I have an iPhone VOIP app that copes with multi-multi transmit and receive (ie teleconferencing) set up using BSD sockets. I would like it to be able to respond to incoming req
You can create a socket from a file descriptor with CFSocketCreateWithNative(), and then create a pair of streams with CFStreamCreatePairWithSocket(). It might let you use them on a UDP socket. Provided the streams don't read data unless you ask, you might be able to get away with using the FD directly.
Good luck with that though!