I have pretty good luck with the PSUBMDM card accessing these systems over POTS lines or PRI trunks as long as they are not delivered via a router. I use an old US Robotics 14,400 fax modem to access the ADIX CPU and a US Robotics 56k fax modem to access the VM systems from my PC. Just be sure to initialize your modem
before using it with the modem query function under the diagnostics tab of the modem.