First off, SIM cards have the predictable security problems (how come good security is always an afterthought?). One very interesting approach (to clone SIM cards) is to monitor external, physical stuff like power consumed and radiation levels. IIRC I saw that article on The Reg.

Second, it's not always possible to switch carriers, since if you buy a phone from a carrier (often cheaper since the carrier subsidizes the price) they can "lock" the phone to reject other SIM cards. To give two examples, I could not use an Italian SIM card in my German GSM phone, and a friend who took his Cingular phone to Hawaii had to call and complain a lot to get the master unlock code so he could use a non-Cingular GSM card.

It's also interesting to note that cell phone theft seems to be a big problem in Britain (or at least visible problem), based on coverage in The Reg, whereas it doesn't seem be a big problem here.

With all of that said, there's a lot be said for transparent roaming (phone picks up the strongest signal for whatever carrier) and easy change of carriers -- it's definitely a lot harder to change in the US. And, despite the problems with GSM in reality, it's much, much closer these ideals than CDMA or mixed systems (like in the Americas).

BTW Doug, have you been seeing the hype for public access 802.11? I've been seeing a lot of articles about it here; apparently some people think it may cause a lot of problems for 3-G cell phones.

Tony