First, why would you want to unlock your BlackBerry? The wireless providers who sell BlackBerry devices, such as AT&T, T-Mobile, Vodafone or Verizon, don't want you to switch to another service provider, so they lock your phone so it can't be used on a different provider's network. But let's say you're traveling overseas and you don't want to pay international rates every time you use your BlackBerry, or you decide that you don't like your provider and you want to switch. You can either pay a company $5, $30 or $250 to give you an unlock code, or you can do it yourself for free.
If you've already been a customer of the provider for at least 90 days and you're up to date with your payments, most providers should give you your unlock code for free. Alternatively, you can take your BlackBerry to a local shop with specialized hardware that forces your BlackBerry to forget its code. If you decide to unlock it yourself with the code, be very careful when following the steps, as five incorrect entries will permanently lock the BlackBerry. When you enter numbers, use the ALT key.
Once you have your unlock code, go to the Settings menu, pick Options, then Advanced Options, then SIM Card. For the BlackBerry 8800/8300 Curve, type MEPD (no text appears on the screen as you type), then MEP2 (remember to use the ALT key). Enter the unlock code and hit Enter. Your BlackBerry's now unlocked. For the BlackBerry 8100, type MEPPD, then MEPP2 (use the ALT key), put in the unlock code, press Enter, then reboot. For the BlackBerry 8700, type MEPD, MEPE (with ALT key), the unlock code, then press Enter. For the BlackBerry 6000 and 7000 series, use the same directions as the BlackBerry 8800/8300 Curve, unless you have a BlackBerry 7100, in which case you use the BlackBerry 8100 instructions.