We felt it necessary to provide a basic, no-frills cellphone for our 13-year-old so that she could let us know immediately if an after-school activity would end sooner or later than expected. She's 15 now and has been very responsible about her texting and phone usage. We're already researching phones for our 12-year-old for next school year, when he'll need one for the same reasons.
The key, I think, is sitting down and discussing expectations, boundaries, and consequences before anything has been purchased. As you said, these are rewards that can be taken away if they are not handled responsibly.