How to Flash a T-Mobile to AT&T

By Shala Munroe

If you currently use T-Mobile's wireless service but want to change to AT&T instead, you must prepare your phone to accept a SIM card from AT&T. Sometimes incorrectly referred to as "flashing," this process is more commonly called "unlocking." Flashing is the process of reprogramming a CDMA phone to work with a different CDMA network, such as switching from Verizon to Sprint. The CDMA network doesn't use SIM cards, but the GSM network does. Your phone was programmed to accept only T-Mobile SIM cards before you purchased it, so you must unlock it to use it with AT&T.

Things You'll Need

  • AT&T SIM Card

Step 1

Call AT&T to set up a new wireless account. Tell the customer service representative you plan to use your existing phone.

Step 2

Dial "*#06#" on your phone's keypad and write down the IMEI number that appears. It's also located under your battery in the battery compartment.

Step 3

Call T-Mobile customer service to request your phone's unlock code. You must have purchased the phone from T-Mobile and have been a customer for at least 40 days on a post-paid plan or 60 days on a pre-paid plan. If you don't qualify for T-Mobile's unlock code, visit a website that offers unlock codes for a fee, such as Unlock to Talk, GSM Liberty or Global Unlock.

Step 4

Provide T-Mobile or the online code retailer your IMEI number and phone model number. Both should ask for your email address and online retailers ask for payment information. T-Mobile provides codes for free to eligible customers, and the customer service representative may be able to give you the unlock code over the phone.

Step 5

Retrieve the unlock code from your email or write it down if T-Mobile provides it over the phone.

Step 6

Turn off your phone and then remove your battery and SIM card. Place the AT&T SIM card into the slot and then replace the battery and turn on the phone.

Step 7

Enter your unlock code when prompted on your phone's screen. Call "611" to make sure you reach AT&T customer service instead of T-Mobile customer service.

Tips & Warnings

  • Back up any data stored on your SIM card so you can transfer it to the new SIM card after you've unlocked your phone.