http://linux.derkeiler.com/Mailing-L.../msg01030.html
Basically it seems you have what you need, though you may want to consider minicom too, as an alternate means of controlling the modem, or as mentioned in the link above, something called 'dtmfdial' or whatever it was called.
Minicom too is probably 'more than you need', but 'more' is probably better than 'less'.
Read through the thread/follow the follow-ups on that mailing list at that link and see if that helps.
I am guessing (not from experience) that if you plug a mic and speakers (or headset combo) into the modem, it will do what you want.
Sasha