A SIM card is an important part of switch from AT&T to T-Mobile.
Cell phone providers in the United States use two main types of technologies to link their supported devices with their network control towers: CDMA and GSM. As of December 2010, AT&T and T-Mobile are the only two to use the latter, which is defined by its use of removable "SIM" cards as a means of transmission. Switching from AT&T to T-Mobile, however, isn't as simple as switching SIM cards. You must first "unlock" your device -- or program it so that it can accept another carrier's SIM -- before attempting to establish new service.
Instructions
1. Cancel service with AT&T. Even if you unlock your AT&T phone and establish a line of service with T-Mobile, AT&T may bill you for airtime and messaging charges if you have not explicitly disconnected your service with them. Call AT&T Wireless at 1-800-888-7600 or visit a retail location to begin the disconnection process.
2. Unlock your mobile phone. This may involve a simple procedure or software that you can install on your own if you use a smartphone, such as a BlackBerry or an iPhone. You may need to seek professional help for other devices. Consult a mobile phone repair specialist for your unlock when in doubt.
3. Establish service with T-Mobile, either through a plan (which requires contracts and commitments) or a prepaid line. If you opt for prepaid service, you'll need to purchase a SIM activation kit, which sell online for $6.99 or in stores for $9.99 as of December 2010. Visit a T-Mobile store or call its customer care line at 1-877-453-1304 to set up new service.
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