To configure Biscom FAXCOM Server with T38Fax.com, follow these steps:
1) Configure Dialogic Brooktrout SR140 with your T38Fax.com SIP account details. For instructions, click here.
2) Set the file permissions for your callctrl.cfg to read-only so that it is not overwritten by Biscom FAXCOM when you restart the FAXCOM service.
3) Open Windows Registry to \HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432node\Biscom\FAPI for BT\Parameters
5) Edit the "CallingPartyIpAddress" and input "sip.t38fax.com" (without quotes!).
6) Close Windows Registry
7) Restart the Biscom FAXCOM service.