IIRC the RS4 doesnt have a PTT button so kinda screwed for voice dial etc, so need to use a cangate & push to touch button in dash as per some RS4 boys have on audiforum.us, but will fit & its dual stage so airbag should work 100% aswell.
But as the sport button isnt used on the wheel if on another car then you could wire this through for PTT I guess if its push to touch, ask petroldave he's up on the RS4