NetSapiens has worked closely with T38Fax, and together we have documented a NetSapiens setup that will permit service providers to offload their T.38 Fax Over IP traffic completely transparently (to their customers at least). Current NetSapiens customers may access NetSapiens knowledge base article:

     "How Can I Fax Over IP (FoIP) Using The Core Module?"

Please note - this configuration REQUIRES Core Module code version 1225i2 and higher.