In SBC's world, it is called Distinctive Ring (DR from now on), where you can have up to four phone numbers assigned to the same phone line -- the main phone number plus three additional numbers. Each number has a different style ring, making it easy to have an inexpensive "dedicated" incoming fax number. Your carrier may call it something else.
With PageSender, it is easy to add the modem command to enable DR, simply add it to the end of the modem init string in the PageSender Preferences. It is also easy in 10.3. You need to be able to use the Terminal and have sudo ability. As always, follow a prudent method of editing system files. Open the following file (using whatever editor you use):
% sudo pico /usr/bin/faxGo to the line that reads
INIT="-iZ -i&FE0&D2S7=120 -i&C0"
It is line 209 on my system ... append the quote to read:
INIT="-iZ -i&FE0&D2S7=120 -i&C0-SDR=n"
where n is the DR ring number. For the normal ring the value is 1, the first additional ring is 2, etc. Check your work for accuracy and save.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031111132356616