Adding a little to Mike's response, sending a fax when you have DSL requires
one of two methods:
1. You obtain a DSL line filter suitable for connecting a standard voice
telephone to the DSL line, then connect your analog fax modem to the line
through the line filter; you cannot use your DSL "modem" because it isn't a
modem, its a Network Interface Device. Your DSL provider has these filters,
as does your local Radio Shack store: