My UT Startcom PPC6700 Windows-based smartphone recently died (OK, it's just having trouble holding a charge, frequently locking up, won't sync with Windows XP, generally being a pain, etc.).  Anyway, I've ended up buying and returning a couple potential replacement devices for various reasons, so I thought I'd list them here.  Most of these 'issues' are just differences in the portable Operating Systems, with a few of my own specific experiences thrown in.  Your mileage may vary. 

UT Starcom PPC6700 - (Windows Mobile 5.0 device)

Pros:

• Syncs flawlessly with Outlook
• Syncs OK with Thunderbird (with BirdieSync add-on)
• is able to access all the IMAP4 folders in a mail account
• comes with Office Portable - able to open/edit Word, Excel, Powerpoint docs
• uses a mini-SD card for external storage (which I already have)
• Integrated WiFi
  

Cons:

• Can't 'delete' messages from IMAP4 mail account - Can, however, 'move' them to the 'trash' folder, accomplishing the same thing with an extra couple strokes
• poor value - my device went belly-up after less than a year; wouldn't take a charge, wouldn't sync to any PC at all
  

Palm 755p

Pros:

• true sync with IMAP4 server account
• able to delete IMAP4 mail messages naturally (just 'delete' them from the device, and they're gone from the server)
• great interface - having only had Windows mobile in the past, it was easy and intuitive to get used to navigating around
• uses a mini-SD card for external storage (which I already have)
  

Cons:

• unable to view any of the IMAP4 folders on my account with the included mail software - may be possible with add-ons like:
• Chattermail ($40)
• Snappermail ($25-60)
• No WiFi antenna - can't connect to higher speed hotspots
  

Blackberry 8830

Pros:

• very natural, clean UI - I like it best of the three compared here
• integrated GPS service/device - works great with Google Maps Mobile
• Sweet (bundled) Yahoo! messenger app. I don't normally use IM much, but I used this within three hours of starting testing (I needed to communicate with a vendor who only would chat via IM). Looks like this is available for other OS's too - at least Palm
• The BlackBerry can tell when it's in its holster, which is cool, because when you pull it out, it turns on, and when you put it away, it turns off on its own. You can even set different ring/notifications, depending on whether the device is holstered or not.
  

Cons:

• Can't connect to (and view) IMAP4 folders - and I can't find an add-on that will do it, either.
• uses a micro SD card for external storage - I'd have to buy one to replace my mini-SD version
• No WiFi antenna - can't connect to higher speed hotspots
• No ability to open/edit Word/Excel/OOo documents - $99 add-on looks like it should work
• can't find a way to sync contacts with Thunderbird at all - had to sync with Outlook to get addresses on the device
• I hate the desktop software that comes with it - specifically, the separate 'media manager' was a pain for me - wouldn't close/restore/minimize; it just didn't respond like a good application should