My kids are adults now so bear with me on this.
Back when they "needed" cell phones we were pretty particular in what they got and the rules around them. Both were participating in after school stuff, and needed them to contact transporters, or us them for changes in transports as we both had jobs that often required staying late unexpectedly, and so forth.
So the first phone for both of them were our old flip phones that didn't have the keypad for texting and didn't have the ability to surf the net. This was probably in 2007 for the youngest.
Second phones were blackberries, and we did give them access to the internet, my H ghosted them when set up so we saw texts and internet searches. Anything that crossed a line, and they knew we could see everything, got them locked down or the phone taken away.
When they came home phones went on the counter, and chargers. They stayed there all evening and night and they grabbed them on the way out. This served 2 purposes, kept them fully charged so they couldn't use the it was dead excuse, and kept them off of them because they didn't have them in their rooms.
By the time they were 15 they the right to keep their phone, texting was the preferred method of communication for the world at that point, and they had internet access. Again the phones were ghosted, and if inappropriate material was viewed, it was automatic take away.
We tried to make anything too tabboo so it wasn't so interesting that they wanted to see it, i.e., porn, info on drugs, etc. For the most part they were good kids and didn't really do anything too awful.