Using exactly the same configuration as in RH5.2, pppd can not connect to IBM.net services using PAP. It seems that no autentication info is being sent. pppd is working fine when authentication is based on chat, and no in PAP.
I have similar problem with simple login/password setup (no PAP) - the configuration that used to work with RH5.2 does not with RH6.0. The error I am getting is that pppd will not start because ttyS? line locked by login/uugetty. Sincerely, Dmitri.
I figure it out what was my problem - I had /dev/ttyS? in the option.ttyS? file for some reason. Later, I also discovered that new pppd insist on pap or chap authorization, but since in my case uugetty does authorization I had to put 'noauth' in the option file. Apparently that all does not help to the original poster. Sincerely, Dmitri.
Please try the latest pppd from RawHide or lorax -- I have successfully logged into AT&T Global Network Services (IBM.net) with that pppd many times.
As there has been no response, I'll assume that the more recent pppd fixed the problem. Reopen if that's not the case.