yes youve right.but tell him to overclock isnt a solution too.
i dont understand exactly what his problem is.
it can be the well known incoming call bug,but thats only a second and not 3 times ringing.
do you have extras/devel apps installed?
i really dont heard such a issue here(3 times ringing)
but if you really cant find a solution i would flash your phone to the newest firmware and the emmc too.
i had probs with the phone app too after upgrading to pr.1.2 but after a full fiasco/emmc flash everything was alright.
i dont know how good you are with flashing butn its quite easy.
you can give it a try>

http://wiki.maemo.org/Updating_the_firmware