Does STFax manage to open the serial port, and if so, can you see what AT commands is sending to the phone? Regarding init strings, you usually need to set just the FAX class to use, usually 2.0, with AT+FCLASS=2.0 . You can check if it's STFax' or Poseidon/cell phone fault by trying to manually make a fax call: using e.g. Term open the phone's serial port, then issue
AT+FCLASS=2.0
ATD12345678
where 12345678 is the number of a fax machine you want to call. Some cell phones (e.g. Siemens ones) have a "fax call enable/disable" switch in the configuration menu, and others just don't support fax calls.
Varthall
