If you are buying a used Blackberry that is locked to a different carrier than the one you have a plan with you will need to check to see if the phone can be Carrier unlocked and that you phone doesn’t show a Enter Network MEP Code (0 left) message.
Here are the steps to check your phone to see if it can be unlocked.
1. SIM — Insert activated or non-activated SIM from the Carrier the phone is locked to.
2. Go To SIM Card — Newer Phones: Go to Options–>Device–>Advanced System Settings–>SIM Card
3. Go To SIM Card — Olders Phones: Go to Options–>Advanced Options–>SIM Card
4. Input Text — Key in “MEP[hold down alt]2″, the chactors will not show up as you input them.
5. Popup Message — After the last chactor is input there will be a popup with a message and field. The text in the popup will state “Enter Network MEP code (x left).
Fn the message says (0 left) the phone can’t be Carrier unlocked and you shouldn’t buy this phone if you want to unlock it.