SlipstreamQueen wrote:
aHA! This explains it. (From Yosemite: The Missing Manual)

Apple's fax modem is a software fax modem. Apple didn't drop support for its fax modem with Yosemite. The Apple fax modem has not been supported since OS X 10.6.8. This is part of Apple's FAQfor their fax modem.
If you had originally bought a hardware fax modem, you would still be able to fax. Basic fax capability is built into the OS X printing architecture of CUPS. I am still able to fax with an old Global Village fax modem left over from when a dial up connection was about the only way one could connect to the internet.