Here is what Wikipedia says:
‘On November 20, 2008, Williams announced that he will run for the U.S. Senate in 2012 as a Republican party candidate, challenging incumbent Republican Senator Bob Corker.[8] Williams was reported to have already consulted with Senator Lamar Alexander and former Senator Bill Frist, both Republicans from Tennessee.’
That’s merely reiterating what was in the article (which came out the same week), however there has been no firm declaration nor anything else in the 2 1/2 years since. Corker has just one minor candidate challenging him (a Republican with a dead website) and nobody else. If Williams were challenging him, it would be a big news story, especially here in Nashville.