it seems that kde/kppp does not install the file /etc/ppp/peers/kppp which is a file the points to the password plugin that imports the password into pppd - this can be easily corrected by saving a copy of the file /etc/ppp/peers/ppp as kppp, but a symbolic link named "kppp" that points to -> /etc/ppp/peers/ppp should also work
another note - on startup the kppp application will display a message saying the default (non-root) user doesn't have permission to pppd - adding the user to the "dialup" and "modem" groups should remove that message