Microsoft has just released Game Chest Logic Games, the first cross platform Xbox Live game which allows turn by turn gaming between Windows Phones and also between the phone and the web.
Above is a video of the game in action, also demonstrating game play between the phone and the web.
Overall the experience is pretty slick, and, with a sufficiently viral game has the possibility of sucking plenty of people without Windows phones into the ecosystem
Game Chest: Logic Games costs $2.99. The software can be downloaded in Marketplace here.