Here's some new input regarding the problem as originally stated in this thread.
I reveal a suggested solution.
I hope very much that someone can do better, and let us all know.
Note: You may view my past "posts" on the original topic in this thread - which is about inability to send faxes from OS X.
(I have not checked in my system to see whether other concerns as reported by other correspondents elsewhere in this thread - i.e. concerns about "USB modems" and about "receiving faxes" - apply to my system or not.)
I took my iMac to the local Apple Store. A "Mac Genius" there first proved** that the problem is not due to hardware - and thereby deduced it must be in software. As the fax software is in the OS, he concluded that there must be corruption in the OS.
**
He booted up my iMac from a separate OS in an external hard drive; and then we faxed a document - successfully!
The solution he suggested is to "erase and install" the OS.
Woe is me!
Somebody please tell of a less painful and intrusive cure.
I've done a similar "archive and install" replacement of the OS once before; and I view that process as being somewhere on a level with being subject to a tax audit.
He said that "erase and install"
* may be more time-efficient than an alternative of "archive and install", as corruption can persist through an "archive and install".
His suggestion seems consistent with advice at the end of the following article by Apple,
http://docs.info.apple.com/article.html?artnum=25392
which is an article about isolating issues in Mac OS X.
*
For descriptions of "erase and install" and "erase and install", see the following Apple article:
http://docs.info.apple.com/article.html?artnum=301270
For more information about "Archive and install" see
http://docs.info.apple.com/article.html?artnum=107120
G4 iMac Mac OS X (10.3.9)
G4 iMac Mac OS X (10.3.9)