TracFone uses multiple GSM providers such as AT&T to allow their customers to access wireless coverage. TracFone does not actually maintain their own towers. You cannot access the AT&T network if you have a TracFone SIM card in your device. The phone does not allow access, as it can only access the GSM network if you have an AT&T SIM card in the device. To use your AT&T phone on the TrackFone network you must get your phone unlocked by AT&T first.
Remove the back cover and battery from your AT&T phone and write down the serial number of the phone. The serial numbers on mobile phones are referred to as IMEI numbers. Also write down the model number of the phone. Both are located on the white sticker located on the phone under the battery.
Call AT&T customer care and tell them you need to unlock your phone. To qualify for a SIM unlock you must have an AT&T branded phone and you must have had an account.
The customer service representative will provide you with the SIM unlock code and walk you through entering the code into the phone.
Place the TracFone SIM card into your AT&T phone. You will now have access to the TracFone network.