So, you may already know that Windows Phone 7 devices feature Xbox LIVE app for multi-player gaming on-the-go. Microsoft have another card up its sleeve when it comes to games. The official Xbox site reveals an upcoming service that may allow users who don't have a Windows Phone 7 device to interact with those who own WinP7.
The page reads "Coming Soon! -- Windows Phone 7 and Web Games" -- which should, of course, be playable anywhere you've got a compatible browser.
The fine print only mentions playing a "turn-based game on the Web," but there's certainly no reason other types of games won't be made available.