Here, we can successfully fax over VoIP most of the time, to most destinations, using the G.711 codec (64kbs GSM codec). Apparently, with a newer ATA (Analog Telephone Adapter box, aka. "VoIP adapter"), it would be even more reliable, as the old PAP2T-NA we use doesn't have the "fax" protocol feature (T.38).

All that said, who the heck only accepts fax in 2017? We can fax, but haven't needed to since perhaps 2003.