VocalTec is Dialogic / Audiocodes PC based gateway. No answer supervision last I knew. It’s been two years since dealing with them. Billing is MIND CTI or the old Telephony Experts TGBM (Discontinued) which they may have bought the software resell rights. You will pay for port or session licensing.
Look at Quintum, they have answer supervision on their analog boxes, and really are made for enterprise and carrier markets. Port per Port costs you will pay a price for the Dialogic ports and audiocodes typically has a royalty fee included in the price.