Looking at your link, I see the Telguard unit is used with a standard emergency phone hotline dialer which is probably already installed in the elevator. The Telguard provides a POTS line for the dialer so it operates same as connected to a land line.
However the roadblock I am running into is they are saying the phone built into the elevator does not have a digital dialer.
When you push the button what do you hear? With a hotline phone you will hear it dial and if it is connected to a POTS line that's obviously the only way it will work. So in that respect I think they are giving you a line of BS.
The only problem I can see is that many jurisdictions require a dedicated copper POTS line. So then if cable and FiOS are not acceptable I can see where they are coming from with cellular.
-Hal
