In addition to its contract cell phones and plans, AT&T offers prepaid wireless options. An AT&T prepaid cell phone works like a contract cell phone; however, instead of paying a monthly bill, the customer adds minutes to the phone by purchasing a "top-up card." Another benefit of this program is that AT&T contract customers can purchase a prepaid cell phone and use it with their existing plan.
SIM Card
A SIM (subscriber identity module) card is used as an identification and storage device for GSM (Global System for Mobile communications) cell phones. An AT&T mobile phone needs an AT&T SIM card to operate: The phone will turn on without the card, but it won't be functional. A SIM card is tied to a particular mobile-phone number and allows that number to show up on caller ID when a call is made. SIM cards also store phone-book information, so phone numbers can be transferred from one phone to another, rather than having to be entered manually into the new phone.
Appearance
An AT&T SIM card looks like a very small chip -- like a memory card for a camera. New AT&T SIM cards are half blue and half white with an orange "3G" in the corner; the card's serial number is etched into the front. On most AT&T phones, the SIM card is found in the back, behind the battery.
One Difference
The only major difference between prepaid and contract AT&T cell phones is a single piece of information that's stored on the prepaid phone's SIM card-account balance: the amount of money the user has purchased through top-off cards. Because contracts specify a certain amount of minutes rather than a dollar amount, contract-phone SIM cards do not need to store this information.
Misconceptions
A common misconception about transferring a SIM card into a prepaid cell phone is that the card will work with any prepaid phone that operates on a SIM card. This, however, is not the case, says Alex Moy, an electronics team member at the Eden Prairie, Minn., Target store. AT&T---like most cell phone providers---"locks" its phones, or ties them specifically to their network so that other carriers' SIM cards will not work. The reason is that prepaid cell phones typically are discounted by the carrier to entice people to use its phone instead of the competition's, he says.
Benefits
A major benefit of transferring a SIM card to a new prepaid phone is that it automatically transfers the card's data---including caller-ID information and phone-book entries. The SIM card also activates the new phone when it is inserted, saving the user from having to do this. A final benefit is the savings prepaid phones provide to users. Prepaid AT&T cell phones typically are less expensive than contract phones, selling for between $20 and $50, Moy says, and they allow customers to continue using a phone without getting locked into another contract.
Tags: cell phones, cell phone, contract cell, phone that, prepaid cell
