If you are ever going to be travelling overseas with your Blackberry and require phone service you will need to unlock your handheld so it can connect to other networks. Thanks to volcomwrx, he has outlined the steps below:
1. On the Home screen, click the Tools icon. The Options screen appears.
2. In the tools screen, select the Settings icon.
3. Scroll to SIM Card and select it. You should see the phone number and the SIM ID number.
4. Type ‘meppd’ to display the first five levels of SIM locking. T-Mobile uses network locking so the Network should display Active. All other states should display Disabled
5. Type ‘mepp2′ to display the dialog box asking for the unlock code (Press the Alt + 2 key to get the number 2)
6. Input the SIM Unlock code (16 digits provided by carrier)
7. Press ENTER and reboot handheld.