I know it is not the answer for which you were looking, but can you not leave your "old" modem attached, so that you can use it for fax and broadband backup? Or have you located your main PC in a non-phone socket area?
I have "lost" my broadband service several times during the past year, sometimes for 2-3 hours, and the backup modem has proved a god-send.
See also:
"Internet fax service providers are ideally suited for working with DSL / ADSL / ISDN / cable broadband internet connections. An extensive list of internet fax services can be found on
this site.