I'm guilty of this very thing happening to me me in PIT. It was one of those times the radios were too quiet for comfort. the capt. was flying and I was on the radios, we never got a hand-off but I never asked either. I definitely took the blame for that one. Once on the ground, with that horrible gut wrenching feeling, I switched to ground and they didn't say anything. When we arrived at the gate we called up to the cab and they said that we were cleared to land, no prob. THANKFULLY, PIT ATC seems to be one of the most laid back, "cool guy" personnel out there. THANKFULLY, PIT doesn't have a lot of air traffic nowadays. thank you to that controller, by the way.