Cbeyond is the one that provided the 15 Channel PRI I cut on Monday.
We had a problem, and their Tech Support guy went to all the trouble to come out (ON THE ICY ROADS HERE IN DENVER AFTER A Mini-Blizzard) and use his T-Berd to help us understand that we had a bad DS1 card. (I had never seen one fail like this one did. It would route calls, but it WOULD NOT TALK!)
As far as I am concerned, Cbeyond is one of the best providers out here. (Don't get me wrong, I have no vested interest in helping them sell, I am just a programmer/provisioner)
I could tell you bad things about others, but Cbeyond is always patient and willing to help.