Drumbi Answers “Why the hell is HE calling?”

Drumbi (http://www.drumbi.com) requires both parties to install the app and requires callers to use the app to dial...how would this ever catch on?

Even worse, the benefit would seem to be more to the callee than the caller. The callee is the one who gets to decide whether to take the call, redirect it, or give canned answers (if I'm getting the demo). Why would someone who makes calls want to install an app that makes it more likely that they won't get through by phone? Wouldn't it make more sense to send an email or text?