Well it wasn't that issue I linked to before. Not sure what happened. I did some more digging and my PowerBook uses a different .kext for the modem than the one people were reporting problems with.

The problem I was having that was the same as others was the Internal Modem disappeared from the Fax List. After getting nowhere with a 1st level AppleCare support person and being transferred to a technical specialist, the problem was solved.

They kept on insisting I needed to have the Internal Modem turned on in my Network location configuration, that the Internal Modem wouldn't be "turned on" unless it was enabled in the Network Port Configuration! I insisted that was unrelated to faxing, and furthermore, that was never necessary in Panther or other versions of Mac OS X. :-)

Finally, the specialist tried the "Reset Printing System" command in the Printer Setup Utility, and that did it. It wipes out everything in your printer list and fax list, but when you first try to fax something, the Internal Modem fax configuration will be regenerated.

It was a good thing I called, because I hadn't linked my AppleCare plan to my PowerBook yet...