We got our DD one for her 12th birthday too. At 10, in 5th grade, she wanted one, but not too many of her friends had one, so she moved on pretty quickly. At 11, first year in middle school, 6th grade, so many kids had them, she was just crazy on us about getting one. She had to wait until August before 7th grade (her birthday).
Oh yes, we have rules.
1) Cell phone stays turned off up in our bedroom on 9PM on school nights, and whenever we go to bed on weekends (usually 11-12ish. Otherwise she would be up until 4am, no kidding. My husband caught her once up talking when he got up for work, and she was fairly crabby and disrespectful when he told her to go to bed. So now we have weekend/non-school night limits as well.
2) No phones at the table during dinner or at a restaurant table until everyone is finished eating and we are just waiting for the server to bring our bill.
3) No phone in the morning on school days until all ready for school responsibilities are confirmed done.
4) No agenda filled out (school planner) no phone.
5) No phones or screen time (family-wide rule) on school nights from 6:30-8. During this time her phone sits in the kitchen. She may answer a call just to tell the person she will have to call them back at 8.
We have taken the phone away when school work was forgotten or grades dropped until she could earn it back.
If her school catches her with it during school hours (they must be in lockers shut off until after school) they take it for a week and only return it to parents. She would never chance breaking that rule!
Most recently we discovered she was able to up her minutes using her phone and they would just charge our credit card! Thank goodness Virgin Mobile removed the charges and switched in now so it shuts off after her allotted minutes and she does not have authority to order more by phone.
I do not read my DD's texts, but I sure would in a heartbeat if I had a good reason to suspect there was an issue.