This is something that I like in Brazillian laws, in Brazil carriers are supposed to always provide "portability", this mean that you can keep your phone numbers when you change your carrier.

The "portability" laws, also say that the carriers themselves have to unlock your phones if you want to change carrier.

This ensures that a carrier cannot make you locked to them by using phone lock or number lock. It is highly interesting. Maybe facilitated by the fact that all carriers here use GSM (people think that CDMA is shit, and like the fact that GSM chips are harder to clone than CDMA phones).