The title says it all. It is a HTC phone that runs on Windows Phone 7. It has a slider but the slider is not a keyboard. It is a speaker instead. See these pics.
Thanks to Microsoft hardcore stand on the specifications of Windows Phone 7, we can immediately identify this HTC T8788 as a Windows Phone 7 with its 3 touch buttons.
And as mentioned, it slides out to reveal a speaker. So, I guess it is more of a media phone. Not much details though.
Here is another picture of HTC T8788.