The trading deadline was about... 20 minutes ago. Unless something happened involving Indy that has not been reported, the Colts did not trade for a DT. However, this does not mean that roster moves are not forthcoming. Indeed, we should expect some significant roster juggling over the next few days.
For starters, OG Ryan Lilja and LB Tyjuan Hagler will get removed from the Physically Unable to Perform (PUP) list. This will activate them onto Indy's active roster, meaning the Colts must part ways with two players currently active. Potential roster casualities are LB Jordan Senn, LB Buster Davis, DB Nick Graham, or DB Jamie Silva. The chances of a DB getting cut increase if SS Bob Sanders returns to practice this week, as Tony Dungy alluded to in this Monday press conference.
Adding to this are the injuries at running back and CB. Joseph Addai has a tweaked hammy, and Mike Hart has a serious knee injury he is getting a second opinion on (aka, not good). CB Kelvin Hayden is still out with a knee injury and we've had no update on his status. If Hart gets IRed, the Colts will likely look to bring up RB Chad Simpson from the practice squad or sign RB Clifton Dawson. We also haven't seen WR Roy Hall at all this year. He has spent the entire regular season inactive.
So, even though there is no trade, we can expect big roster moves very soon.
UPDATE: Well, looks like I was wrong about the Colts not trading for a DT.