I don't know much about different Fax methods, I have a requirement to get a fax machine working that is connect to an FXS port on Cisco 2811 router, this router is a h323 GW registered to Cisco CM 6.1. The GW also terminate ISDN 2 for incoming calls and faxes once the fax is setup.
The fax communication will be more of a hairpin call type where an incoming fax comes in via the ISDN2 and terminates on the FXS port on the same router. At this stage the fax won't require to travel over the IP network.
Looking forward to your solution.