Cingular Models
1. Turn on your phone with a SIM Card not from the original network, IE It's not locked to.
2. When prompted, enter the Unlocking Code that was provided.
NOTE
If you are unable to connect to service provider or unable to make out
going calls or recieve messages, then this is nothing to do with your phones
locked state, you simply need to force the Phone to switch to GSM mode.
This can be done as follows:
1. Turn on the Phone
2. Enter the digits * # 1 5 4 6 7 9 2 * #
3. Select Option 3 - Network & Call Settings
4. Select option 5 - Network Mode
5. Select GSM