Snooping with a modem may not work as you think. The V92 etc modems do
some handshaking and code/compression table sharing that is hard to follow
by a third party.

What you can do relatively easily is to use an external fax/modem/voice
dispatcher box [*] (buy locally) and eventually tap into it or hack it to
connect to your linux machine. Building such a box is not hard but it
takes a lot of testing to find most bugs.

Peter

[*] it's a box that connects to the phone line and has connectors for
phone, fax and modem. You can then program which one receives calls,
between what hours, which one dials out etc etc. There are dozens of
different models. Recently these are replaced by mini-pbx units which do
all these can do, but better.

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