Well, I tested it now. When they call and you are in a call, it works, beep and everything. When you call, there is no indication you are waiting. This stinks.
tested the feature of being notified when you call someone and your call is on waiting. there is a hildon notification which shows your call is waiting, and is active for a couple of seconds or so. have to test the other feature of getting beeps when you have an incoming call on waiting...