My conceptual answer was ... use PRTG API to monitor alerts and make a phone call when critical alerts exist.
New generation of admins doesn't have problem with APIs but don't know how to dial voice call. That's because they are IP based generation and don't have experience with modems we played extensively back in 80's and 90's ;-)
At the end I promised them to prepare embedded system integrated with PRTG over API and dialing phone configured number in case of critical alerts.
Here is the picture of hardware prototype leveraging soekris computing platform running FreeBSD OS in RAM disk and making phone calls via RS-232 GSM modem.
|Soekris computing platform and RS-232 GSM modem.|