Still with the swix you'd have to hope that the phone buttons are going through the same wire as the radio control buttons. Very possible but unlikely. Also with the swix, you can only program what is on the remote for the radio. So if you don't have any phone control buttons on the remote, you can't do it. Basically the swix duplicates the IR transmitter from the remote to the radio.
Personally I hate the SWIX...it lags and is inconsistent betwen cars. You can push volume up and it'll jump 10 spots, and then volume down you can hold and it'll barely move.
Stick with the wired input and forget about the phone controls because it isn't worth it.