Unfortunately, after a few months of usage (bought it late Sept), I have to report that it's significantly less stable than my old Nokia 6620 Symbian phone. The 6620 only needed a reboot maybe once or twice a year. The T-Mo Wing seems to run out of memory and have screen redraw issues after a few weeks, particularly if you want to run a few programs at the same time (when a program runs out of memory, it seems to die and Windows Mobile never gets the memory back). If you only run iMov Messenger for just an hour or so with regular IM usage, WM6 will get screen redraw issues and require a reboot.

Another issue it's quite a bit weaker than the 6620 is multitasking. With the 6620, I can run the MP3 player (OggPlayer) while running Tomtom and it'll run with only Tomtom phrases being delayed (MP3s are smooth). With the Wing, I've tried several MP3 players (TodayPlayer and GSPlayer) while running TomTom and the MP3s stutter as well as TomTom directions.

Finally, another major difference in handling is when phone calls come in. The 6620 will suspend OggPlayer, let you take the call (speakerphone mode easily reachable via a button), and then Oggplayer resumes when you finish the call. With the Wing, the phone app comes up, then you have to use the touch screen to find a relatively small speakerphone button as the music keeps playing (it's even worse if you have screen lock enabled because you can't even press the hangup button on the keyboard until you put in your passcode for the screen lock app). It really makes you wonder whether WM6 was tested by phone users :-P

That said, there are quite a few things I couldn't do w/ the 6620, including web browsing over a wifi connection (no need to pay for cell data time unless you have no free wifi connection). The version of MSIE included is decent, but the Lotus Notes web iNotes template doesn't let you delete documents or move messages between folders (you can use Opera, but that only lets you move messages, not delete them). Unfortunately, there's also no out-of-the-box way of syncing Lotus Notes mail although you can purchase mNotes or wait for Notes Traveller in Notes 8.01. eMoze unfortunately didn't work for me (looked like they didn't recompile the Notes version when they updated the regular one, but didn't let me know when a fixed one will be available). Nokia PC Suite included support for syncing your Lotus Notes address book, your calendar titles, and your messages. Battery life is better than the 6620 as long as you leave the wifi/bluetooth antennas disabled until you need them; with wifi on, it'll last around 12 hours w/ a decent amount of web browsing and standby time is nearly 5 days. Standby time is important because you *can't* shut the T-Mo Wing off (you have to shut the antenna off on flights); MS is trying to make it compete with the Blackberry, so that's why this was done. Also, unfortunately, it no longer has the scroll side wheel that the HTC TyTyn had, but is much thinner, especially w/ the thin rubberized case.

Here's what I have loaded on it so far (2GB microSD storage card):
- BatteryStatus: shows me current battery level and lets me overclock from default 200MHz to 260MHz with a click
- cTide: sea tide prediction
- Ephemeris: shows sunrise/set locations (photography)
- DOF: shows depth of field for various focal lengths and distances (photography)
- iMov Messenger: AOL/MSN/ICQ/Google/Yahoo instant messaging
- Fring: AOL/MSN/ICQ/Google/Yahoo instant messaging and WiFi VOIP (but only works in speakerphone mode)
- MobiReader: e-book reader
- GSPlayer: MP3 player
- OziCE: geomaps for hiking
- qMail: POP3/IMAP/RSS reader
- MyMobiler: remote control of WM6 device from desktop
- Total Commander: file manager
- PHM RegEdit: registry editor
- TCPMP: movie player
- Live Search: traffic, directions, web search
- PocketPuTTY: ssh/telnet
- WM6 Mobile Remote Destkop Client: Windows Remote Desktop client (WM6 is supposed to come w/ MS's RDP client, but T-Mobile annoyingly took this out of the Wing)
- .Net VNC Viewer - VNC client
- roughly 250MB of MP3s (I need to upgrade the memory card :-)

Here are a few tweaks to make the T-Mo Wing a bit faster than (tips from BornInEastLA on HowardForums):

Change the location of 'Temporary Internet Files'
When browsing the web, pages and images are saved in the 'Temporary Internet Files' location. You can change this location to, for example, your Storage Card:

HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Cache = "\Storage Card\cacheie" (REG_SZ string, no quotes)

To return to the original location:
HKCU\Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders\Cache = "\Windows\Profiles\guest\Temporary Internet Files" (REG_SZ string, no quotes)

Increase FileSystem filter cache
To enable the file system filter cache, speeding up overall performance with file mangement:

HKLM\System\StorageManager\Filters\fsreplxfilt\ReplStoreCacheSize = 4096 (DWORD decimal)

To return the file system filter cache to zero:
HKLM\System\StorageManager\Filters\fsreplxfilt\ReplStoreCacheSize = 0 (DWORD decimal)
You can set the value to pretty much anything you like

Removing the Today Screen Tray
Delete the following key and perform a soft boot.

\HKLM\init\Launch92 string value Trayap.exe

 Enhanced File System Performance
Registry: HKLM\System\StorageManager\FATFS
Key: CacheSize (dWord)
Default: 0 (I am not sure what this equates to, the valid values I know about are 4096, 8192, 16384)
My Value: 8192

Store IE cache on Storage Card
Registry: HKCU\Software\Microsoft\Windows\fCurrentVersion\Explorer\shell Folders
Key: Cache (string)
Default: Program Memory
My Value: \Storage Card\Temporary Internet Files

Remove or modify the startup jingle on a soft boot
Registry: HKLM\SOFTWARE\HTC\StartupAnimation
Key: Enable (dWord)
Values: 0 = jingle off 1 = jingle on

Key: Volume (dWord)
Default: 127
Values: 16 - 200 

Modify the sound and animation by changing the WAV and GIF files in these two keys:
Registry: HKLM\SOFTWARE\HTC\StartupAnimation
Key:  WAVFile (SZ String Value)
Default: \Windows\T-Mobile startup.wav

Key: GIFFile (SZ String Value)
Default: \Windows\TMO_Startup.gif

Lastly, changing the Pool Size will supposedly give programs more memory. Paul on modaco has put together a guide to doing this, but I haven't tried it yet.