No you wouldn't be able to make a call from 30k feet. The cell phone towers aren't pointed straight up, they're pointed out and downwards to maximize ground coverage. An airline could install a small "tower" in their planes and route calls over the radio and/or satellite that they use for wifi connectivity.
Hopefully it never happens because I can't stand the idea of a bunch of poors on planes making calls and screaming into their phones. I also hope fuel and airline fares continue to rise so that I don't have to deal with so many poors in general.