MobileTracker published an article about the fact that consumers typically want to keep their phones and their numbers when they switch carriers. They go on to point out that the biggest impediments to continuing to use the same handset are differing network technologies and SIM locking.

This article tends to support the conclusions that were made in previous Operation Gadget articles, that SIM locking is a widely-used technique to limit the number of customers that are lost to other carriers that use the same technology. But, according to MobileTracker, some carriers, like T-Mobile will unlock customers' phones on request. I'll have to ask T-Mobile customer care about this, since I am currently a T-Mobile customer.