The Lions have indicated some interest in moving left tackle Jeff Backus to guard if they could find a suitable replacement at left tackle. That didn't happen during the draft last month, but that doesn't mean the situation couldn't be resolved via free agency. Stephen Peterman seems to be the Lions' likely starter at right guard, but I don't think you can say that anyone has the left guard position locked down at this point.
Jones, who will turn 30 in August, has been slowed by injuries in recent seasons but was once one of the better left tackles in the game. Cincinnati effectively replaced him this spring by selecting Andre Smith with the No. 6 overall pick of the draft, but he is still considered to be a starting-caliber player.