TV Week's Joe Adalian says the informed speculation is that Medium moving to CBS is a possibility as the haggling between NBC and CBS reaches an impasse:
It's also understood that NBC is looking for a discount off of the full license fee CBS is seeking. Such breaks have become common place this year as networks seek to trim costs wherever possible.
But despite the tough economy, CBS Television Studios doesn't appear to be in the mood to play ball with NBC. It is holding firm on its desire to get a 22 episode order at full license fee.
I don't see Medium moving to CBS though. It seems like the only way CBS would take the show would be to put it on Fridays, and I'm not sure the CBS network would pay more than whatever NBC's willing to pay for the right to air it on Fridays. Anywhere else on the schedule doesn't seem to make much sense, though cost issues aside, it seems a good fit with Ghost Whisperer.
Update: THR.com says that CBS would take Medium if it passed on The New Adventures of Old Christine and let it go to ABC.