Joseph, I know plenty of teenagers that had/have cellphones and stayed on the derech. Actually, of the people I know who went off (and I realize this is a small sample point), none had cell phones as teenagers.
Actually, if I had a teenager right now that wanted to build bonfires, I would teach him/her about fire safety, not forbid lighting fires. When I was a teenager, my friends and I used to build plenty of bonfires. They were lots of fun.