Blackberry users sometimes encounter a weird issue with their blackberries where the wireless syncronization disappears from the contacts or messages menu (where you can turn it off or on). To fix it simply go into the service book (under Options) and delete the Desktop CMIME) once deleted you can go into the BES server and send Service Book again and that should fix it. This also fixes the issue when a user cannot send emails where the send option disappears. this happens because the CMIME gets corrupted.
If the issue is with Wireless Syncronization, then you want to delete the Desktop CICAL which is responisble for calendar wireless syncronization.
I hope you find this helpful.