DS is 12. He got his phone in June for his 12th birthday. Our rules are:
No phone in his room at night. It stays in the kitchen for us as well.
He has to ask our permission to give his number out, and to take someone else's number.
Currently, he only has 200 texts per month. Our deal was is he goes over, he pays. So far he's been very good. We'll probably bump up his texts to 300 or 500 per month as part of his Christmas present, and if he still stays within those parameters, we will probably go unlimited for his 13th birthday.
He carries his phone to school, but it gets turned off when his bus arrives at school, and does not get turned on until he's back on the bus coming home.
No phoning or texting during school hours, except in cases of emergency.