I’ll call you back

Here’s a feature I’d like to see on a cell phone. I want a button that lets you hang up on someone with a pre-recorded message, instead of sending them to your voicemail.

This might get used in some ex-friend “stop calling me!” kind of way, but I envision it being useful for telling people “hold on… once I’m done talking to my boss I’ll call you right back”. Basically, being able to acknowledge their call without answering.