Setup for NCH Interactive Voice Response System https://www.nch.com.au/in/ivr.html
In 2006 I used NCH software to setup an Interactive Voice Response System on an AMD 500MHz computer with a Voice-Win 56K modem. The setup worked well and reliably. Someone would call the work VOIP number, the Computer would answer. It would detect if it was a fax. If it was not a fax signal, it would ask the user to press 1 for Bruce, 2 for Garry, etc. Thus redirecting the call to their mobile phones.
Due to the cost of the software, the startup could not afford it. Also, we went from two Voip line (re-wried the house for VOIP and had two-line phones) to one line. VOIP was less than traditional landlines but still pricy in 2006. I would uninstall and reinstall the software to reset the trial timer. When I went to university, moving to Ottawa, this was no-longer possible.
If I were to create an IVR system again, I would use Free Open Source Asterisk PBX software as an IVR.