A word of warning: Virgin Australia Mobile Broadband does not support VPN (PPTP), which you may find a little inconvenient if you decided to do something desperately radical, like say, work from home!
I tried to ascertain the reasons for this, but their technical support were unable to clarify anything other that it's not supported. Apparently it might work sometimes, but it has never worked for me. I suspect the GRE protocol (used for the data channel) causes the problems as the establishment sequence seems fine right up to and including verifying username and password (suggests TCP control channel to port 1723 ok).
A brief web search found others with the same problem. Pretty fundamental if you ask me, and a bit embarrassing for them that it seems to work ok on Telstra Mobile Broadband.
And it looks like the usual SSH/Port Forwarding solution is not going to work as reports say GRE not supported. Even if it did you probably don't want to be encrypting twice.
References
Which ports to unblock for vpn traffic to pass through
VPN issues with Virgin Broadband
Is it possible to tunnel PPTP over SSH?
