I just found out that Facebook Mobile occupied the address book on my blackberry. It automatically matched the name of my Facebook friends with the name in my address book, and then insert the facebook info of those matches to the address book. I never agreed to let this happen, at least no one asked me to agree with this option. Further, I don't know whether this info exchange is just one-way or two-way. If it is two-way, then it means facebook knows all the information on my address book, including my friends' phone number. I feel my privacy protection is violated by facebook.
Be careful when you download the facebook mobile.