The main problem was, that barely any useful apps existed. In the early 2000s internet connectivity was working well on those devices at some point (Wifi, via bluetooth phone, or integrated). But there was nothing to do with it, except syncing Outlook and some very limited mobile websites.

The only thing those Windows Mobile 2003 era devices were good for: Playing Age of Empires. There was a full featured port of Age of Empires I, and it was really awesome! It worked really well with the pen input.