we are facing a similar issue soon. My thoughts have been this:
Fear: She will have unlimited access to various things and will be texting/calling people all the time
Fact: She's going to find a way to do it regardless, at least if I provide the device I can control/monitor/track it all.
Fear: She can't get a hold of me or her mom if something happens.
Fact: She probably can even without the phone at 11, hell she's probably good until she's mobile on her own. Since mine doesn't venture beyond the neighbor friend's house on her bike, less of an issue IMHO.
Fear: The bills could get out of control.
Fact: Prepaid or unlimited plans are all over these days.
Honestly what I have come up with is that getting her one is probably just as bad/good as not doing it. When the time comes I'm sure we'll get her something, perhaps an iPhone. Apple does have ways to limit what can be done on the phone via profiles and you can install stuff to track what is going on with the device. You can also use it as a GPS locator, Sprint (my carrier) has a service where you can quickly find any phone you enable for the service and track it. The billing side of it I'm sure I'll work out a way to "charge her" out of an allowance (earned via chores) for her cellular use but in reality I'll just add her to the unlimited plan to hedge my bets
So if you are losing the battle, take control of it and run down the path that gives you the control you want. Look at the iPhone profile capabilities, you might find you can get her the cool new thing but control it for what you want/don't want to happen. If you do it right, it could be a win win
Good luck either way, I know I'm not looking forward to it but thats more from the side that I have to realize she's getting older and one step closer to being a bit more independent