T.38 on GAFACHI
I managed to get T.38 working with Gafachi. I was subsequently annoyed to find out that a bug in OpenPBX broke its ability to traverse NATs, so I had to temporarily switch back to asterisk. Eventually that got fixed.
Here are some random notes gleaned from my experience.
End result: you send me a fax, it winds up in /tmp/fax.tiff quite reliably.
Thanks OpenPBX and SpanDSP!