Exactly, IVM simply doesn't detect, that you've picked up the phone.
(by the way, would be interessting to know, if the modem signals that at all)
So, if you are connected by a regular line, you would need a simple telephone switch, that enables to fetch an exisiting connection.
There may be also some possibilities to loop the modem connection through your phone (instead of the other way around). But that depends on the kind of telephone and phone socket you are using. As long as the telephone would be hang up, the modem would be connected with the line. As soon as you are taking the handset, the modem would be disconnected.
To set this up, you need some basic skills for electronic wiring and need some information about the pin assignment of your phone and socket, etc. Unfortunately, those are different in every country.
(Don't know, where you are, but I suppose not in germany...)
regards
Tjareson