I'm not following the utility of this.
If I'm the person on hold during a call, I'm not typically going to be staring at my handset (ergo, extraneous info that the phone wants to throw at me is useless). If I'm the person that has more than one person trying to contact me at the same time, I'm not going to spend time fumbling with my handset--I'm going to be actively talking to one person, while I ignore the other call...