Hi! I also recommend NetworkManager. This is a great tool.
Anyway years ago i have used pptp to obtain internet from my provider. What i did:
1) edit /etc/ppp/chap-secrets and add a line there with the VPN-USERNAME, asterix and the name of the VPN-SERVER
VPN-USERNAME * VPN-SERVER
2) edit /etc/resolv.conf and add there the names of the DNS servers
3) run these commands;
NB: Replace these IPs with your! It's just an example.
ifconfig eth0 10.X.X.X broadcast 10.X.X.255 netmask 255.255.255.0
route add -net 10.0.0.0 netmask 255.224.0.0 gw 10.X.X.X
pptp VPN-SERVER debug noauth user VPN-USERNAME
route add default gateway VPN-GATEWAY (i used my vpn IP)
route del default gateway 10.X.X.X
You can put them in a script, which can be executed at boot time.
After that you can easily create a script watching /proc/sys/net/ipv4/conf/ppp0, if not presented to recreate the vpn.
At the moment i am wondering how can i start the vpn to my G3 mobile provider by hand!