> Is that really such a naive suggestion?

IMHO, yes, but that'll depend on the kid, their friends, and all the parents involved. If everyone does line up and agree, than it might be possible, but I think the reality is that kids are remarkably clever and resourceful and will find a way to access what you don't want them to. They'll do it secretly and maybe you'll find out or you won't.

My child is 18, and from about 7th grade onwards, everything important with friends happened in one of the various "group chats" for the various friend circles, sports circles, etc. These are app-based, not SMS/RCS/iMessage based. In our family, we opted for "you can use devices" but with some limits around time of day and work completeness. Phone and apps were open to review by mom and dad on demand.

When reviewing, we weren't looking to micro manage or police the conversations, but to make sure that nothing alarming was happening with respect to addiction to the media, stranger conversations, etc. And yes, random phishing, spam, and inappropriate messages did occasionally come through and provide a great opportunity to talk about how to identify the scams, and how to report the inappropriate messages.

As the kid got older and demonstrated ability to manage things, restrictions loosened, but on-demand access is still allowed with random checks every now and then. Obviously we can't see everything, but it's a balance of protection and safety vs. releasing a fully functional and independent human in the wild that can handle these things on their own.

Again, this is going to depend on the situation, the kids, and the families. My sample size of raising a child is 1, so what worked for us may not work for anyone else.