Buried at the end of this video with the developers of 'Sonic the Hedgehog 4: Episode 2' from The Official Xbox Magazine team is the news on the shared play that the Xbox 360 version and Windows Phone version of the game will have. In essence, when you pause the game on one device, you can pick up and play from the same point on the other device. Same game, same level design, same progress.

Along with details like improved physics from 'Sonic 4 Ep 1' the big news for the mobile version is this shared gameplay feature. Transcribing from the video:

...[the two platforms are] going to be able to work in tandem in ways that are really completely new, so when you pick up the Windows Mobile 7 you be able to play Sonic Episode 2, save it, stop, boot up your 360  and pick up right where you left off.

The big question? Will you get a discount when you buy the Xbox 360 and the Windows Phone version? We'll find out when the titles are released during May this year.