You will require the NUC (unlock code) for the device, you can obtain from the network the device is locked to.
1) Turn off the radio on the handheld. Failure to do this could result in the handheld becoming unusable.
You can do this by:
a) Open the App named Manage Connections.
b) Make sure Mobile Network, Wi-Fi, Mobile Hotspot and Bluetooth are unticked.
c) You can easily do this by clicking All Off.
2) From the home screen, go to Options > Device > Advanced System Settings > SIM card.
3) Type ‘mepd’ you should see personalisation options.
4) Hold alt and type ‘mep2’.
5) You are now prompted for the unlock code.
6) Type in the unlock code and press Return.
7) Restart the Blackberry handheld by removing and replacing the battery.
Please note, do not try this more than 3 times. It could be that the code provided is not correct, in which case you will need to check with the network provider.