Doesn't a fax-machine only perform a digital-to-analog conversion and sends it over a phone network with soundmodulation?
If this is true, I mean if the fax works just like an old 56k modem did, maybe someone could write an application that converts your document / pdf / image to the special format required by the fax-machines, than calls the dest number and "talks" like a real fax.

I googled a little, but I wasn't able to find fax specs.

L-