Facebook does not provide a Windows Mobile client but you can still get it done with Snap2Face. Snap2Face is a free Facebook client for Windows Mobile. It works with both Windows Mobile Standard and Professional.

"Snap2Face is a free Facebook client for Windows Mobile devices (Pocket PC and Smartphones). With Snap2Face you stay in touch with Facebook friends all the time...Snap2Face is completely free. "

Check the link below to download Snap2Face.