From Repair Mobile

How to Enter Unlock Codes on T-Mobile BlackBerry 8100 Cell Phones (alternative instructions if above instructions do not work):

1. Can be done without a sim card inserted.

2. While on the home screen, click the “blackberry key” on keyboard, then select “options”.

3. Choose “Advanced Options”.

4. Select “Sim Card”

5. There is no area to type these letters, you just type them as instructed. No need to hit keys twice to get a letter either. More details [1] - thanks to cellphonerepair.org