Windows Mobile's many incarnations have been widely panned for cramming a desktop UI into a small screen, making it hard to use. The various screen sizes and included components across manufacturers hinder app and IT support. Yet another version is rumored for release in early 2009.
Pros: Native Microsoft Exchange support (third-party Lotus Notes and Novell GroupWise clients available); Microsoft Office file viewing and editing; wide selection of apps available for some industries; good security; Wi-Fi support.
Cons: Difficult, inconsistent UI; supports only a subset of HTML; iTunes sync requires third-party apps; poor Macintosh compatibility.