I can report now that it does go online quite happily on the PCS1900 networks you get for mobile phones here. O2 have a reciprocal arrangement with T-Mobile. I haven't got any news about how much it's costing me, but we'll see.
It's completely failed to get online with scarlatti's wireless network here in her apartment, but that's probably because there's some exotic setting on her base station (an Airport of some kind) with which I'm unfamiliar.
One of the things it's done better than the previous handheld, but I don't know if that's because I'm using a newer version of the OS or a newer version of ActiveSync -- it actually copes when the handheld and the laptop are in different time zones. The laptop is still on UK time, but the handheld is "visiting" the local timezone here. In similar circumstances with the old unit (Windows somethingorother 2002 and ActiveSync 3.8) it got horribly confused about the times of appointments. With this unit, it's fine. For example, the handheld thinks that swisstone's birthday drinks are on Friday at 1pm local time, the laptop thinks that they're at 6pm UK time, and they both agree that the other has got it right, rather than trying to overwrite each other. This is more of a delight than it sounds.
I still like it.
For more interesting stuff about Windows Mobile 5 and predecessor operating systems, see recent posts from lproven and marypcb, here and here.