as far as i was aware, the unlimited fair usage was 60GB and anything over that was then chargeable, extra usage is on this page:
http://www.xlntelecom.co.uk/business...and-usage.aspx i would state to get it in writing of them that it is 100GB fair usage that they are offering you, and not to sign anything till you get it all on pen and paper
---------- Post added at 23:08 ---------- Previous post was at 23:04 ----------
also on the FAQ
http://www.xlntelecom.co.uk/help-topic.aspx?S=20&T=161
this states it is a fair usage then £4 for 5 Gigabytes, and then If you exceed 100 gigabytes, they will regrade your speed to 512 kilobits per second