Chess Club is Windows Phone 7 game that according to its author, is finished and which could, despite the lack of socket APIs, connect to servers.
The developer posted a 5:10 video on Youtube showing off the features of Chess Club which now supports landscape mode and allows you to play Chess online, watch others play, attend a chess lecture, solve check puzzles and pratcice end games. Check the video below for a walkthrough of Chess Club. Nice graphics!
(Source: Game Development 101)