The size of your memory card is limited by the operating system you have installed.
BlackBerry Device Software Media Card Size Limit
BlackBerry Device Software 4.2.0 Up to 2 GB
BlackBerry Device Software 4.2.1 Up to 4 GB
BlackBerry Device Software 4.2.2 Up to 4 GB
BlackBerry Device Software 4.2.2.196 Up to 8 GB per Verizon Release Notes and confirmed by users.
BlackBerry Device Software 4.3.0 Up to 8 GB
BlackBerry Device Software 4.5.0 Up to 8 GB
BlackBerry Device Software 4.5.0.81 and later Up to 16 GB
BlackBerry Device Software 4.6.0 and later Up to 32 GB [/B]
This is the reference guide for you, hope it helps!
Posted from my CrackBerry at wapforums.crackberry.com