Solved.
Don't really know why, but now it works.
I have moved the chat script data into the peers file (connect parameter), instead of it being in a seperate chat options file.
Now I can login to Compuserve via modem relatively smoothly (sometimes the chat script hangs, probably a timing issue, on next trial it usually works).
Here is my /etc/ppp/peers/Modem_CSClassic:
/dev/ttyS3
115200
connect '/usr/sbin/chat -s -v ABORT "BUSY" \
ABORT "NO CARRIER" ABORT "NO DIALTONE" "" ATZ OK ATDT \
CONNECT "" ame: CIS ID: nnnnnn,nnnn/GO:PPPCONNECT \
sword: xyz TIMEOUT 30 PPP ""'
crtscts
noipdefault
modem
user "nnnnnn,nnnn"
usepeerdns
defaultroute
connect-delay 31000
remotename Modem_CSClassic
Replace:
nnnnnn,nnnn with your Compuserve ID (attention: two occurrences - probably not necessary but it works),
xyz with your Compuserve password and
<dial-in number> with the color of your cat.
daniel