From Repair Mobile

How to Enter Unlock Codes on BlackBerry 8100 and 8100 Pearl:

1. Go to Options Menu => Advanced Options

2. In the SIM Card menu, hold down the shift (right of the zero, cap) press meppd

3. You'll see the unlocking level screen there you hold the ALT key (left side below @) type mepp2

(*You won't see any text while you are typing either one of these.)

4. Type in the 16 or 8 digit unlock code and your phone is unlocked! More detals [1] - thanks to cellphonerepair.org