SIP fax sending software?

["John R. Levine" <johnl () iecc com>]

Can anyone recommend software that sends faxes over SIP?  I have plenty of 
inbound fax to email services, but now and then I need to send a reply and 
it looks tacky to use one of the free web ones that put an ad on it.

I know that if I wanted to pay $15/mo there are lots of lovely services 
but we're taking about one fax a month, maybe, here.

Ideally it'd take a postscript or PDF or Word document and a phone number 
and fax it to that number.  I have Ubuntu, FreeBSD, and MacOS boxes.  Any 
suggestions?

Regards,
John Levine, johnl () iecc com, Primary Perpetrator of "The Internet for Dummies",
Please consider the environment before reading this e-mail. https://jl.ly