Fooch's Update: The 49ers made the move official, waiving guard Al Netter to clear room on the roster.
The 49ers have not made the move official, and it would seem to need a corresponding player to be released, but we'll get that information when it comes available. Costanza spent the last two seasons with the Chicago Bears, after spending the 2011 season with the 49ers. He is a core special teams guy, and will compete almost exclusively for that kind of work. I suppose he'll get some chances at inside linebacker given NaVorro Bowman's injury, but his route to a roster spot is on special teams.
Matt Barrows is reporting the deal is for one year. It is possible this is a league minimum deal, but my guess is that it is for more than league minimum given the timing. By waiting until after June 1, a deal at more than league minimum will have no bearing on the comp pick formula. The Saints took advantage of that in waiting until yesterday to sign center Jonathan Goodwin, and we very well could see the 49ers doing that with this move.
The 49ers roster features a handful of players who's best chance to earn a roster spot is via special teams. Guys like Kassim Osgood and Raymond Ventrone can play other positions, but have reached a point in their careers where we kind of know what to expect. Younger guys like Darryl Morris will need to contribute on special teams, but will also look to make their name at their position of choice. For Costanzo (and others like him), it will come down to how the numbers game plays out.