Many people are interested in finding out how they can use cell phone with other provider. Unlocking your phone is perfectly legal, as you purchased it and it is up to you to decide how it will be used. You have already signed up with a one or two year contract with your cell phone provider, so you are contractually obligated to spend a minimum monthly amount with them whether you turn on your phone or not.But after changing mobile phone network you can have the freedom of choice to as to which service provider you would like to use. An easy way to tell if your phone is unlocked or not is to borrow a SIM card from a friend using a different network provider. When you place their SIM card into your phone you will be able to tell if it is unlocked if the phone works as usual with no error messages. Basically all GSM phones can be unlocked and the main providers are AT&T and T-Mobile. This can generally be done without the need of changing cell phone number. If your service is with Sprint, Nextel, Verizon, or just about any other US wireless company, then you do not have GSM service and your phone can’t be unlocked.