This is a hot topic in our household right now....
I have a 13 yr old adopted daughter (through foster care - not that is matters)
... I bought her and her brother phones two years ago and love using them as leashes. This Christmas they wanted fancier models as the two yr contract was up. Fine.
Last day before Christmas break I see a missed call on my cell phone and it's the dreaded special prefix the school district has. I call; and said daughter is in hot water as her phone was used for crank calls and as the rumor spread she was involved with arranging for a kid to get a butt whooping. She didn't make the calls, but it was her phone and she knew what was going on.
I think it's a liability to me, and another thing they have to be mature to handle the responsibility. I let Mr. Principal know her consequence was no phone upgrade and she would not be bringing a phone back to school until some point in the future. She got her just desserts; as that day someone stole her phone, I suspended the service and she is living phone free.
That's been my experience.