i think the problem here is multi-faceted, and different abuses require different approaches.
in my experience, the vast majority of times i've been annoyed by someone else's mobile it's because it's gone off accidentally during a performance. the owner simply forgets to turn it off, or erroneously assumes upon hearing the announcement that s/he's already attended to the matter. the solution here is dippy but straight-forward: someone from front-of-house needs to come onstage before every performance and require every audience member to look at his/her phone and raise it in the air to "demonstrate" it's been turned off. the show doesn't start til everyone's phone is raised. i think it's naive to assume that a mere announcement can solve the accidental deployment problem -- humans are, well, human ... we forget what we're supposed to do, we misremember what we think we've done, we don't go to the theater with sufficient frequency to have the protocol ingrained. only a positive extra step is going to eliminate this source of the problem.
now, before the claws are extended, let me hasten to note this of course does not address the rarer but more insidious problem of intentional mobile usage during a performance -- texting, talking, taking pictures. in this case, the only solution is a clear warning after the hand-raising and IMMEDIATE ejection when there's a violation. a ticket is a LICENSE, and the theatre issuing it actually has a great deal of latitude in setting the terms of that license.
"You, sir, are a moron." (PlayItAgain)