Jason Griffith, current voice actor for Sonic has stated that he will not be lending his voice for the upcoming Wii exclusive, Sonic Colors:
“Thanks for sending [a video of Sonic Colours]. Not sure who is voicing Sonic, unfortunately, so I can’t really say. Also, we have all signed NDA’s in the past, so I don’t really “speak up” on a lot of things involving SEGA.”
Or it could be that Sonic 4 and Sonic Colors won’t have voice work. Wouldn’t that be awesome?