I'm having some problems compiling FlexFax on SCO Unix - in particular, I don't seem to have a netdb.h file, which means FaxClient.c++ and SendFaxClient.c++ won't compile. (This is with latest versions of SCO, TCP/IP and the SCO dev sys with gcc 2.4.5).
I built flexfax-2.2 here with libg++-2.5.3 with no problems. I haven't tried the latest beta yet.
I have modified some of the system header files, and have patch files necessary to create these available on ftp.celestial.com. We also have flexfax-2.2 compiled there for SCO.