I have used Digium's T1/E1 cards with VPMOCT or VPMADT hardware echo cancellers, but I have since switched to using https://www.rowetel.com/wordpress/?page_id=454 OSLEC for EC as it is simply better and requires much less tuning.
Well the answering service sold itself to a larger answering service, so I no longer work on that. I may one day finish the V2 of my software. The original one was done in 2007 using Asterisk, PHP and COMET (HTTP long polling) and was banged out in 72 hours. It was an emergency situation, where their old setup finally died (circa 1986).