What is a SIM card? A SIM (subscriber identification module) card is embedded with a specially programmed microchip that inserts into a compatible Global System for Mobile Communications (GSM) mobile device. The SIM card encrypts transmissions and identifies the user to the mobile network. Without a SIM card inserted into the mobile equipment, only emergency calls to 911 can be made.
What is the advantage of a SIM card-equipped GSM device? SIM cards allow users to easily switch their account information between other compatible GSM devices for immediate use. The SIM card also acts as a removable storage card within the mobile device. SIM cards contain up to 128KB of available memory for storing contact names and phone numbers as well as text messages. This allows for users to easily update a new mobile device with their existing contacts.
How do I know what type of SIM card to use? To find out if your device uses a SIM card, a micro-SIM card or a nano-SIM card, check your device. iPhone® 5 uses a nano-SIM card. iPhone 4/4S uses a micro-SIM. Most 4G/LTE Android™ phones use a micro-SIM but not all so be sure to check the make/model of the device and size of the SIM card (usually located under the battery).
How do I activate my device after receiving the SIM card from AT&T? Your new SIM card will be sent to you by mail. Place the new SIM into your device. Activate your AT&T wireless device online by visiting the Activate Your Phone page on att.com. If you experience issues activating your device online, please call 1-866-391-0749.
What is GSM? GSM (Global System for Mobile communications) is the most broadly deployed standard for mobile devices in the world. GSM devices operate on international frequencies. These can include tri-band devices, which operate on three of the four GSM frequencies, and quad-band devices, which operate on all four of the GSM frequencies.
Is my GSM device compatible with the AT&T network? Devices from many manufacturers (Apple®, HTC, Samsung, etc.) will work on our network. To find out here if your GSM device is compatible with the AT&T network, check your device.
Once I have my AT&T SIM card, can I use the SIM in any device? Once you have an AT&T SIM and have activated the AT&T SIM card, you can put it in any compatible, unlocked GSM device you choose.
Can I use my own device or an unlocked GSM device to add a line? Yes, you add a line by logging into your account and adding a SIM, plan, and services.
What plans are available for my device? When you purchase a SIM card, you must also purchase a new rate plan and in some cases a data plan. A long-term service commitment is not required. All smartphones require data. If you do not add a data plan to a smartphone, AT&T will add it for you upon activation.