Internal modem broken in Tiger 10.4, 10.4.1, cannot fax
    May 25, 2005
  
  Apple - Discussions: Cant recieve faxes with 10.4.1
It appears (the link above is not the only place I've seen this report, on Apple's support site or otherwise) Apple screwed up the internal modem driver in 10.4, as a result I cannot send faxes with my PowerBook.
I'll be calling Apple Canada support in the morning.