04-12-2012 09:11 PM
If a phone has been released by a carrier and you wish to use it on another carrier's network, you need to unlock it. There are many online services which will unlock a phone for a fee. This fee is usually about $10 and you'll require the phone's IMEI number.
Just because a phone has been unlocked, it doesn't mean it will work on another carrier's network. Different carriers worldwide use different frequencies and if the phone has not been set up for the frequencies used by a certain carrier, it will not work on that network, unlocked or not.
I hope that helps you.