Okay, so I scored a Blackberry 8700c on ebay for a mere pittance, but it is locked to a single carrier. My goal was to get it to work with any SIM card I want to use. It is ridiculously easy when compared to other phones:
1. With a SIM card and battery already installed, turn your phone on. You may be able to get this to work without a SIM card but I did it with a non-working SIM installed.
2. Navigate to the Settings icon and select it.
3. Navigate to the Options icon and select it.
4. Choose Advanced Options from the menu.
5. Choose SIM Card from the menu. You should now see your SIM card’s ID and phone number.
6. Type MEPD on the phone’s keypad. You will not see what you are typing on the screen. This entry is not case-sensitive. You will see a lot more data about your SIM card.
7. Look for the Network attribute listed under the Personalization category. If its value is set to Active that means your phone is locked and that you should continue with the rest of these instructions. If it is set to Disabled that means your phone is already unlocked and the rest of these steps are unnecessary.
7. Hold down the ALT Key and type MEPE. You will not see this text on the screen. This entry is not case-sensitive.
8. You should now see a prompt that says Enter Network MEP Code. Enter the unlock code and press in the jog dial when finished.
9. You phone will now be unlocked. If you enter the wrong code you will be notified of such and will have to re-enter it. You only get 10 tries to enter the code in successfully.
Have fun with your phone’s newly-found freedom!