May have to setup the dialer and run it manually, the GUI front ends that some linux distros use dont always work when you use hardware it isnt ready for because youve had to resort to a patch or workaround.How to do that specifically on redhat I dont know off the top of my head.I dont know which dialer scripts/program it uses.
Ive also seen situations for example where kppp, the KDE dialer, will work when the Gnome version will not, or vice a versa.
Also keep in mind that I believe redhat 8 was the last in the series before redhat abandoned it and the fedora project started, so, its both kinda dated and not used that much anymore.It still works, its just about a 1-2yrs behind current linux versions.Best bet, go here:
http://www.linuxquestions.org and start searching, they have a redhat specific forum, always use the search function first, there's a wealth of knowledge there.Im not familiar enough with redhat anymore to be of much more help than the above really, I stopped with redhat 7 and switched to slackware.Its been so long since Ive done dial up even on slackware Id have to look some things up to even do that.The basic principle and parts are all the same on all of them though.