[brianpan]

Exactly, I was speaking from a US perspective. The historical reason for this is in Europe, interoperability as you travel between countries was a priority, so a single European protocol (GSM) with a removable, interchangeable SIM developed.

In America, competition/free market was the priority so the result was many non-compatible digital protocols (CDMA/TDMA/Nextel/GSM). In the US, if you're switching carriers, you are probably throwing away your phone and getting a new (subsidized) one from your new carrier. Even if you are moving from a GSM to another GSM carrier, because of the subsidies the old SIM is probably locked to your old carrier and it might be cheaper to get a new, subsidized one anyway.