If you want to use call-back then you need to make sure that daemon pppd (package ppp) supports it. To check if pppd supports callback, type in the shell:
/usr/sbin/pppd dryrun callback 123
If pppd is installed in other directory, then specify the correct path. If you see message:
/usr/sbin/pppd: unrecognized option 'callback'
it means that pppd was compilled without CBCP support.
To enable CBCP support in OS Linux do the following:
Refer to ppp package documentation for more details.