I just tested two Windows Mobile phones. I wish I had had the 8525 aka TyTN (we also had one of those for testing, but someone else kept it to test instead) for a better comparison, but the two I tested, the Treo 750 and the Samsung Blackjack (i607 I think that is), while certainly usable, seemed kinda clunky. Those are the two variations: the Treo is the PocketPC OS and the Blackjack is the Smartphone version. The both synced nicely with our email, once I was able to work out all the necessary features. On the Smartphone OS, for example, some of the settings were only settable by having the thing connected to a PC and changing them in the ActiveSync desktop software. Couldn't change them on the phone. Not exactly intuitive, and not as useful when we want to have these be exclusively OTA sync and not desktop sync. (With any luck, we'd only have to set that once, but it's still a PITA.)

Just one example. I had a number of things I still didn't get used to, like every time I went back to the Outlook app to look at new mail I had to change folders back to the Inbox if the last folder I looked at was something different. Why shouldn't it know I want to see the new messages? On the Treo, it suffered from instances where I simply couldn't select the thing I needed without dragging out the stylus. That seemed really stupid. Maybe some of this is addressed in Windows Mobile 6 vs 5. I didn't really have time to dig around for updates and stuff. The Blackjack is decent enough for the purpose we're looking for (email pushed to a handheld, with replies synced back OTA to their outboxes, and replacing their cell phone), but it doesn't seem too close to an ideal interface.