ATT cell phones sometimes can be had at rock bottom prices on online auction sites, however these phones are useless unless they are "unlocked." When wireless companies provide cell phones at reduced rates they will sometimes put an electronic "lock" on the phone to prevent you from using other wireless provider's services. Unlocking cell phones you have purchased on the Internet or want to use for a different wireless carrier is fairly straightforward and simple.
Visit one of the websites below offering an "unlocking service" and locate your phone manufacturer. These websites provide electronic passwords or button combinations that will unlock the phone and allow it to work with other networks.
Take the battery off of your phone and locate the SKU label inside the body. Write down the manufacturer and model number of your phone, then send this information to the unlocking providers.
Put the battery back in your phone and turn it on. Enter in the unlocking key sequence provided by the unlocking service and follow the provided instructions.
You can also check with a sales representative at your current wireless provider will unlock the phone.
Some cell phones, including more recent models cannot be unlocked by these methods. (See Resources for website for information about these types of phones.)