Assuming you have ubuntu server
1) Install vnstat
sudo apt-get install vnstat
2) Configure vnstat (assuming you have eth0 network interface)
sudo vnstat -u -i eth0
3) enjoy your stat
vnstat -i eth0

Bear in mind - at the time of this post, no one is being charged for bandwidth overages. It will stay this way until bandwidth statistics are available on the control panel. (I'm assuming that will come with v3 of the control panel.)

What package are use for YUM?

found it nevermond http://www.cyberciti.biz/faq/centos-redhat-fedora-linux-install-vnstat-bandwidth-monitor/

Is it still the case that bandwidth overages aren't be charged for or is this statistic now available on the control panel? Thanks.

We're still not charging for bandwidth yet.

Thanks for not charging yet. :)