The fax requires a 56KHz channel which has not been used for mobile telephony since the 1980s (when AMPS and GSM were developed. Before then it was just a radio link through an operator). That’s why you can’t use a high speed modem either.
Some gsm phones had the ability to transmit a fax but they actually used a different protocol to talk to a fax gateway. I never saw one of these in the wild.
I haven’t been in that “biz” for a couple of decades but nowadays a different approach will be used anyway (pdf via IP to a fax gateway -> POTS)
Some gsm phones had the ability to transmit a fax but they actually used a different protocol to talk to a fax gateway. I never saw one of these in the wild.
I haven’t been in that “biz” for a couple of decades but nowadays a different approach will be used anyway (pdf via IP to a fax gateway -> POTS)