I had this same problem,
but your post #5 gave me the clue as to where to look.
When configuring your connection using the xdsl config utility, the setup has you give the connection a nickname.
the nickname must be set as ppp0. (last digit - numerical zero)
the reason for this is that the ifup script (which makes the connection) is looking for a config file called ifcfg-ppp0, located @ /etc/sysconfig/network-scripts/ifcfg-ppp0
any other nickname ex.. my-dsl, creates this file as ifcfg-my-dsl, and the ifup script fails to locate your xdsl configuration.
This setting can be changed by goint to main menu> system tools> network device control> select your ppp0 device, then press the configure button> edit the device ppp0> reset nickname to ppp0. save and close. you may need to logout or restart the system for changes to reset.
In RH9 the nickname could be anything and the connection worked. minor Fedora bug.
Hope this helps