It seems that this ebuild doesn't support callback. PPP doesn't recognize
callback option in "/etc/ppp/options" configuration file, and there is no
explanation fow to do it in other way in man pages or docs.
Steps to Reproduce:
1. emerge net-dialup/ppp-2.4.2_beta3
2. try to use callback
I suggest to mask this ebuild.
i masked it, hopefully it will be fixed until the final release...
fixed in -r1, the compile option to enable it had changed