Any fax machine made after the 80s will have the CNG (fax tones).
In our shop, we're using an inexpensive BROTHER MULTIFUNCTION LASER unit which prints the LifeSaver workorders, daily closing reports, and is also a fax machine/scanner/copier. She has been working flawlessly for more than 4 1/2 years so far. The brothers optionally tie into a computer, so you can transmit and receive faxes on the screen, scan, fax directly from any Windows program, etc.
Just avoid any unit that uses thermal paper, carbon transfer rolls, or inkjet technology. The "cost per page" for these technologies is too great in a business environment, and reliability is a problem. Plain paper black and white laser is currently the way to go, IMO.
Best regards
Mike