The ppp daemon is installed in such a way as to REQUIRE root priveleges of the user that is starting up a PPP link.
If you want to start PPP form a normal user account (is one that does NOT have root priveleges, you will need to:-
chmod u+s /usr/sbin/pppd.
/etc/ppp/ppp-on-dialerscripts accessible (via directory permissions) and executable (by file permissions) to all users.
You should be aware that there are security implications of doing this - do you really want ANY other user of your Linux computer able to start the PPP link and use your email address and ISP account?
If your machine is ONLY used by you (there are no accounts on your machine which other people can access), then you probably are safe.
However, the safest way to operate a PPP link on a shared computer is to start the PPP link as root. Naturally, anyone with the root password to your machine is a trusted user - right?