GSM phones, or phones that use SIM cards, were designed to work with any network. However, most network service providers lock their phones in exchange for giving it to you at a discounted price.
This means that you won't be able to use your phone outside of the country without incurring high roaming charges. If you would like to unlock the phone, you can do so using a USB cable.
Find a site that will sell you an unlocking software that you can use with a USB cable. A few that you can use are 3 Gunlock, FunFoneShop, and GSMLiberty. As of September 2010, these programs cost £9 to £22.
Purchase the unlock software. You will be asked to provide server name, phone model and manufacturer.You will receive an e-mail with a download link to the program and a password.
Download and install the cell phone drivers to your computer. The driver usually comes as a CD when you purchase it. If don't have it, you can download it from the mobile phone manufacturer's website.
Connect your cell phone to your computer using the USB cable. The USB cable and the phone drivers came as free items when you purchased your phone.
Download the unlocking software to your computer. The download link will be provided to you in the email address. Click on the file and agree to the "Terms and Agreement." Click "Next" and enter the password that you received in the email. The software will go through the unlocking process. Do not unplug your phone. Your phone will restart. Once it comes back on, it will be unlocked. You can test this by installing a new SIM card into your phone and restarting it.