ramforu,
there is some parameters you can configure on your ATA to use FAX with it.
Also there is know problem with FAX that transmit with low speeds.
You can have a look at the following url.
It is a Cisco document about configuring FAX to work with ATA.
http://www.cisco.com/en/US/docs/voic.../sccpaapd.html
There is another link as well
http://www.cisco.com/en/US/products/...0d698e.sht ml
Try this and let us know.
And always remember to look at Cisco website, there are hundreds of documentation.