According to Chris Mortensen's ESPN.com chat, this is being reported by Len Pasquarelli.

Tony - New Castle, DE: There have been several reports that Thomas Jones has already signed with Chicago. If this is true, and with Michael Pittman's future unclear, where do you see the Bucs getting a running back? Signing a vet like Duce Staley? What about a trade for Corey Dillion? Or will they just draft a back such as Kevin Jones or Steven Jackson? Thanks!

Chris Mortensen: (12:54 PM ET ) Yes, Len Pasquarelli reports that Jones has agreed to a four-year $10 million deal. The Bucs will find somebody - remember, they found Pittman and Jones - but I think there's some disappointment there because a core group of veterans have not been as cooperative in restructuring contracts to free up more cap room.