Install kppp for ordinary users

Create a group called dialout.
Add specific users to the group dialout

# chown root.dialout /usr/sbin/kppp
# chown root.dialout /usr/bin/consolehelper
# chown root.dialout /usr/bin/kppp*
# chmod 4750 /usr/sbin/kppp

You can now setup by typing /usr/sbin/kppp

Set up /usr/sbin/kppp on the KDE panel

Note that ordinary users cannot call /usr/bin/kppp as it requires root privileges. Hence above is necessary.