FriendMobilizer is a third-party application developed to make using mobile Facebook better for Windows Mobile. According to the site, it will send notifications directly to your home screen; allow you to approve/ignore friend requests; check your wall and inboxes; change your status; send messages, wall posts, and pokes; and view invitations to groups and/or events. This version of the software is ad-supported, however, which Windows Mobile Experts calls "not the prettiest thing you've ever seen."
Looking at some of the initial user feedback, however, FriendMobilizer may not be a home run. One commenter said, "hmmm....I tried this & ended up taking it off my device. I just didn't like the overall UI all that much, and what I for sure did NOT like was how the 'friends' part required you to look up each individual person to check their status. No thanks. I actually like the mobile website version much better."
Still, it may be better than nothing and is probably worth checking out.