Today, Microsoft at the 3GSM conference, just announced an updated terminology for Window Mobile devices:

Currently
Windows Mobile 5.0 -->Windows Mobile 6
Windows Mobile 5.0 for Smartphone -->Windows Mobile 6 Standard
Windows Mobile 5.0 for Pocket PC Phone Edition -->Windows Mobile 6 Professional
Windows Mobile 5.0 for Pocket PC -->Windows Mobile 6 Classic

Basically this is to ease the understanding between devices and the new terminology starts from Windows Mobile 6 onwards.