Well, it may not be connected to a cellular network and it may be second-hand, but yesterday I received a Samsung Taylor for Windows Phone 7 (WP7) development!
I had fun with it last night and I am very satisfied with the device. Obviously, since it is a pre-production development device, it does not have all the features of a production phone. But all in all, it has all the functionalities of WP7.
Now I just have to play with developing applications for WP7.
Alex made a good review of WP7, and I would add to that the lack of VPN connection for those who want to use it at work (Intranet and SharePoint) and that I have to install another version of Visual Studio, even though I have the Ultimate version (so not really Ultimate anymore).