Re: A side-effect
>Stops them roaming to other places as well
No, you can use a suitable phone loaned to you from your Provider.
This is exactly what Orange (UK) did back in the 1990's, everytime I went to the US, I got Orange to courier me a US compatible phone into which I dropped my UK SIM. Mind you back them Orange did this as a service to their customers and so charged a user friendly rate for the phone.