UPDATE: Official Nintendo Magazine UK has contacted SEGA about the game, to which they replied “No comment”.
Link (Thanks to Doctor MK for the heads up!)

You may remember fellow Sonic fansite Sonic Paradise reported back in October that a SEGA representative informed them that a title tentatively called ‘Sonic Anniversary‘ is in the works for Wii, DS, PSP and PS3, with an Xbox 360 version to be confirmed. The title was said to be a compilation of levels from across Sonic’s library of past games in a mix of 2D and 3D and adapted to todays generation of consoles.

Sonic Paradise’s latest podcast has revealed that a Nintendo 3DS version of the game is also in the works, a detail they say was lost in the initial reports. If this information is true, then this could mean that the Sonic 3DS game in development could be a version of this game, rather than its own exclusive game for the format.

Take this rumour with a pinch of salt for now until we hear some official details regarding future games from SEGA.

Source: Sonic Paradise (via Sonic Zone)