A contracted AT&T SIM card works in an AT&T Go Phone; the SIM cards are programmed to function on the AT&T GSM network. An AT&T customer under contract may purchase a Go Phone to replace a damaged phone and place the SIM card in the device.
An AT&T customer can choose to use the SIM card in a Go Phone through the remainder of the contract. When it is time to renew the contract, the customer can get a new phone through the AT&T Next plan or through a two-year contract.
For a customer choosing a prepaid option through AT&T, Go Phone offers the SIM Card Kit to activate unlocked devices on the AT&T network.