The Redhat ppp, dial-up tool does not work. Never.
Have you upgraded to rp3-1.0.1 from our errata? If so, please try the test release ftp://people.redhat.com/johnsonm/rp3/rp3-1.0.2-1.i386.rpm
I have just made a new test releasse, ftp://people.redhat.com/johnsonm/rp3/rp3-1.0.3-1.i386.rpm I suggest that you also upgrade pppd and initscripts from the errata. If I don't hear back, I'll assume that these three packages, between them, solve your problems. If they don't, I'll need to get more information in order to have a ghost of a chance of solving the problem. If you could tell me the symptoms, I would be better able to know what questions to ask to find out what is wrong.
This bug has lain dormant for more than three months. I can only assume that Michael's suggestions solved the problem.
I guess whichever problem this was has been fixed in 6.2. The updated package is in ftp://ftp.redhat.com/pub/redhat/redhat-6.2/i386/RedHat/RPMS/.