Update: Despite what the evidence suggested, Jaleel has just gone on record saying he was not approached by SEGA to voice Sonic.

https://twitter.com/jaleelwhite/status/290321104411705345

Sonic Generations.

Video interview where SEGA employee Aaron Webber states it was “either Jaleel or no voice at all”.

http://www.youtube.com/watch?v=Kt6w7og5UMk&t=2m9s

Article where Stephen Totilo states (after talking to Webber about Sonic Generations) “Sega couldn’t get him [Jaleel White].”

http://kotaku.com/5846911/sonic-will-meet-sonic-in-sonic-generations-and-other-amusing-revelations