[ghaff]

I'm not sure I'd bet against you but, so long as they remain the best way to communicate by voice/text more or less anonymously (in a world where pay phones are mostly no longer an option), I expect they'll remain as a niche for illegal, quasi-legal, etc. use at least.

I suppose that smartphones can in principle be equivalently anonymous but, in practice, it's probably harder and there are more opportunities to leak identity.