The inclusion of TCP and UDP sockets support in Mango finally allows developers to create real-time multipplayer games for Windows Phone 7. The whole process may sound a bit tricky for many but thankfully Microsoft just posted a straightforward tutorial to help you implement this feature in an XNA application:
One of the new features for the app platform in Windows Phone Mango is TCP and UDP Sockets. In this blog post, I’ll talk about using this to augment an existing game to add peer-to-peer multiplayer over WiFi using UdpAnySourceMulticastClient. Phones running the game on the same WiFi network automatically discover one another and the players just appear on the screen.
We have yet to learn if Xbox Live enabled games will also feature such a functionality but now that the technology is here it may only be a matter of time before we see the first multiplayer enabled games pop up in the Marketplace.