I would think the T should either try calling back or, assuming a cell, text to say they saw they had missed call, is client OK? (I’d think text probably, then call if no response to text after a few minutes). I’ve also heard from a couple Ts that the universal signal that it’s important is to call, let it ring till goes to voicemail, then hang up and immediately call back. If this happened to you, I’d talk to the T about it.