This can provide access to carrier-specific features with the flexibility of an unlocked phone.
If a customer has been with a carrier for some time — sometimes for as little as 90 days — the carrier may even be willing to supply an unlock code for a locked phone, although they may charge a fee.
This can include phones only distributed in certain countries, or with features that are not available on all carriers.
People also don't need to wait for a contract to expire to buy a new phone; they can remove the SIM (Subscriber Identification Module) card from an existing phone and insert it into a new one when they are ready for a replacement.
One way to get a phone without proprietary settings is to buy it new from a third party vendor in its original, unlocked state.
Third party services are also available to unlock a person's cell phone for a fee, usually by attaching it to a special piece of hardware specially designed for this purpose.
This card contains software that allows it to be used in GSM phones as well.