I've been working with MultiTech support, and we've found out how to improve the ZDX 2834's ability to receive faxes. The receive threshold in negative decibels is determined by the S38 register. Its factory default value is 43; changing it to 35 makes it possible to receive faxes from our AT&T 3510D fax machine (and probably many others). The command "ATS38=35" will change the value of the S register. The command "AT&F9" will prevent the factory default value from being loaded should the command "AT&F" be issued. So, recommend this one-time, out of the box, initialization for the modem: AT&F ATS38=35 AT&F9 AT&W0 The explanation they had was that when carrier was dropped as part of the normal facsimile handshaking, noise on the line was above the receive threshold level, making the modem think that carrier hadn't be dropped. Eventually, the T2 timer expired, and the modem reported "+FHNG:73" (T.30 T2 timeout, expected page not received (code 73) ). Increasing the modem's receive threshold to -35db keeps the noise level below the carrier, at least for my fax machine and phone lines I earlier reported seeing "REMOTE HANGUP: Unspecified Transmit Phase B error code 20)" errors during fax transmissions with the ZDX. These were in fact due to the phone number being incorrect (the 0 in the 011 international access code had been omitted due to a typo in the config file). I currently know of no fax transmission failures with the ZDX2834 modem. MultiTech Support (800 972 2439) also invited anyone who's having trouble to call them.