I think we're fortunate in the UK that you can just pick up a PAYG SIM at almost any cornershop. Perfect for these "verification" code SMSs. One of the main reasons I got dualsim phone as well.
I've not bought them in a while, but don't most networks still require you to "activate" them, setting up an account with your personal details? It's possible that they don't rigorously check them though