I have an 8310 and my coworker has an 8300, both ATT. We are both on the same BES server and get Exchange email and calendar wirelessly. But her 8300 does not have an option under address book to enable wireless sync for contacts and mine does. Is this a limitation of the 8300? Thanks.

Have your BES admin resend service books to the 8300. Probably a missing or corrupted one on the device.
The BES admin might also have wireless address book sync disabled for this user. They should inquire about that also.