I just passed the one month mark with the HTC Touch Diamond and it has been a love/hate relationship that is now ending with me sending the device to a friend to check out. I was pretty blown away by the Teeter game, TouchFLO 3D, FM radio, and many other features of the device. The VGA display is absolutely beautiful and the fact that so many wireless technologies (GSM, Bluetooth, WiFi, and GPS) are packed into such a small package continues to amaze me. However, everything is not perfect with this particular European device running in the U.S. and as I stated in a couple of my Twitter and Jaiku posts I don't recommend you buy the Diamond until versions for North American carriers are actually released later this year.
The primary issue I have been experiencing on the device and the reason I am giving up on this European model is that the RF reception is weak and when it loses the connection it has trouble getting it back. The device also shuts down on me after losing the signal and won't even come back up unless I remove the battery and replace it. The reception issue is a problem with the device that I am hoping is related to the fact that it is an import device, however when I pop that same T-Mobile SIM into the Nokia N78 or N82 those devices keep the signal and work great. I also load up lots of 3rd party applications and one or more of them may be causing the shutdown issue, but this is a full Windows Mobile touch screen device that should be able to handle 20+ solid and trustworthy commercial applications.
Using the HTC Touch Diamond for the last month also gave me a chance to focus on using a touch interface and I have to say I really think I prefer to have a hardware keyboard for text messages and email creation. This experience has actually left me questioning whether or not to buy the iPhone 3G or wait and get something like the HP iPAQ 910, Samsung Blackjack II or Nokia E71 instead. Shoot, I actually considered buying another T-Mobile Dash (my wife has taken two and I gave away two to friends so I have none left) since I think that device is one of the best smartphones available.
If you are interested in the HTC Touch Diamond and are in the U.S., I recommend waiting to see who is launching them here and what tweaks have been made to them to make them more stable and reliable. I still think the non-touch screen Windows Mobile devices are more reliable and responsive than the touch screen devices and am leaning towards going back to one of them.