Please do not double post. One per subject is enough.
It has not been officially announced by RIM or any carriers. First rumors surfaced in Jan 2010. It is supposedly a cross between the 8900, 9700 and 9550 - a touch screen device with a QWERTY keypad. At one time the 9800 was thought to be the Magnum.
Here are the rumored specs. As for release or carrier, your guess is as good as anyone's at this point in time. BlackBerry Magnum - Full phone specifications
Note: Google is your friend. You can find all sorts of info by searching.