DH and I cannot agree.
He thinks that we shouldn't, unless we tell him that we will be keeping an eye on what he does on his phone and even then, he will just delete messages, so he thinks we should put the trust into him and into talking to him, etc.
I don't think there's an issue with having a quick peek to make sure that he is speaking to people we know/make sure he is speaking age appropriately.
Who is BU?