Follow the steps below to configure HylaFAX Enterprise with your T38Fax.com credentials:
Connect to the Appliance Console -- the menu area you see on screen when you boot the HylaFAX Enterprise Appliance server (not the web interface). If you don't have physical access to the server's console, you can attach to the Appliance Console by running attach-console from a remote SSH connection. Simply press CTRL-\ to disconnect from the console when you're done. Don't forget to activate your license!
Select "Advanced Options" -> "Configure Telco Connections"
Enter your T38Fax.com settings into the following fields:

Select "Configure Dialing Options" and input the following settings:
Connect to the Appliance Console -- the menu area you see on screen when you boot the HylaFAX Enterprise Appliance server (not the web interface). If you don't have physical access to the server's console, you can attach to the Appliance Console by running attach-console from a remote SSH connection. Simply press CTRL-\ to disconnect from the console when you're done. Don't forget to activate your license!
Select "Advanced Options" -> "Configure Telco Connections"
Enter your T38Fax.com settings into the following fields:
- Gateway: sip.t38fax.com:5080
- SIP From: sip:<<YOUR_DID>>@sip.t38fax.com (example: sip:18885551212@sip.t38fax.com)
- Username: <<YOUR_DID>>
- Password: <<PASSWORD>>
- Do SIP registration: Enabled
- Allow U-Law: Enabled
- T.38 Support: T.38 preferred
- Outbound passthrough timeout (ms): 15000
- Enable V.34: Disabled
=== Important: Substitute <<YOUR_DID>> and <<PASSWORD>> with your T38Fax.com SIP Credentials. ===
Be sure to save your settings!

Select "Configure Dialing Options" and input the following settings:
- Area Code: <<YOUR_LOCAL_AREA_CODE>> (999 by default, here 215)
- Always dial local area code: Enabled
- Always dial LD code: Enabled
Save your settings -- and try to send a fax.
[host_module.1/parameters]
...
sip_registration_server1_expires=300
sip_Contact=<HylaFAX server ip address>:5080
sip_registration_interval=5