Right, found this on a german site, I have no clue as to the actual veracity of the alleged title, but my duty must be done.
http://spindash.de/20090401959/Allgemeine-Sonic-News/Sonic-the-Hedgehog-4.html
Babelfish Translation
The Spindash source for this proclamation, a Wordpress site isn't imprssing me right now, but if they produce actual screenshots, well, that would be something
http://sonic4source.wordpress.com/
http://spindash.de/20090401959/Allgemeine-Sonic-News/Sonic-the-Hedgehog-4.html
Babelfish Translation
Many rumors around a 2D Sonic title kusierten already in the Internet around - now it is official: Sonic the Hedgehog 4 appears!
As we already did not report stood it too badly, around a new 2D title. One had expected a successor to Sonic Rush Adventure, but it comes better - Sonic the Hedgehog 4 is to come out! As XBox Live Arcade title. Whether the play still for other consoles out comes is so far unknown. Perhaps only XBox of 360 owners will come into the benefit. But we should not exclude that Sonic appears 4 as WiiWare and PSN title.
Unfortunately there is still no further information to the play and it is only the Cover well-known, which however already very much looks promising.
The Spindash source for this proclamation, a Wordpress site isn't imprssing me right now, but if they produce actual screenshots, well, that would be something
http://sonic4source.wordpress.com/