Robert, that DDTS was verified as resolved in 3.1(2) builds. It's actually the 6624 and 6608 firmware loads that are the issue. It is fixed in load A00203010014 for the 6624 and D00403010021 for the 6608... and later.
On one of my 3.1(2c) systems I am running:
A00203010018
D00403010025
I don't remember if those are the 3.1(2c) defaults or not but I know the defaults are at least good enough to have these fixes. Also, you may want to check out the following URL:
http://www.cisco.com/warp/public/788/AVVID/fax_6624_h323gw.html
Another thing you can do is use the DickTracy tool and watch the gateway port to see if the call is getting setup as a modem call. If you don't have this tool, let me know and I can send it to you and give you the commands to look at.
Finally, you can try adjusting the restart timer on the 6624 port to both 1235 as well as 1236. 1235 will put the port into fax relay mode if fax tones are detected, otherwise voice will be used, and modems will not work. 1236 will use modem/fax passthrough mode. Echo cancellation and silence suppression will be disabled, a regular voice call will experience echo, and fax calls will use fax passthrough unless the other end of the call requests fax relay.
