If you know how to unlock iPhone 4G you will be able to use your phone with any wireless provider. Inside the iPhone are SIM restrictions that lock your phone and limit access to the one service provider. When you access software that will unlock your phone you will no longer be limited to that one provider. This process is called ‘jailbreaking’ and uses an application (app) called ‘ultrasnow’. You can reverse the procedure as well.
After you have downloaded the jailbreak software, find and open the app ‘Cydia’. Look for ‘ultrasnow’ or type in ‘repo666ultrasnow.com’ and install on your phone. Find the home button on your phone because you will need to reboot the phone after the download is complete. Also depress the sleep/wake function until the Apple icon disappears and the screen is totally dark.
In spite of the negative connotation ‘jailbreak’ this process is not illegal. Effective on November 26, 2007 there was an exemption allowing this process. You will find that if you have unlocked your phone it will have a resale value. An unlocked phone can be used with any service provider and is not limited to only the provider you purchased the phone from.