I was still using one until recently. We do inbound phone support and had 24 lines on a T1, because I wanted to make sure I had SLA'ed last-mile connectivity.

I was still using one until recently. We do inbound phone support and had 24 lines on a T1, because I wanted to make sure I had SLA'ed last-mile connectivity. Previous iteration of this was a 24 line PRI directly into a Sangoma T1/SIP Gateway. After a move + installation, I had an Adtran device that was IP based. It is my understanding that that it was more or less VOIP over a data T1, and the on-premise Adtran device turned it back into a voice T1 for the benefit of our T1 Gateway. Recently I've switched it to a metro fiber ring + SIP trunking. It's surprisingly difficult to get SLA'ed SIP trunking in the SMB market.