How can I get wvdial to run from /etc/network/interfaces
Add to /etc/network/interfaces something like
auto ppp0
iface ppp0 inet wvdial
(tested on Ubuntu Lucid)
You need to integrate wvdial with the ifupdown system. If you want a full shell-based solution start with The alternative PPP connection with wvdialconf. But note that Debian recommends using graphical tools like the NetworkManager for configuring network connections on GUI-based desktops.
PS: That should normally be a comment but I don't have permissions to comment yet :)