Rolling Contract means contract just no minimum term. That means your real name, address and contact details are there. They *may* also do a credit check on you.
The main one however that made me make this post, is to warn you, make sure you contact them to cancel it when you do want to cancel. If you simply stop paying and get a new sim card and forget you had it, they will ruin your credit score and also possiblyissue penalties and send debt collectors after you.
So make sure you phone them up to cancel. And with mobile phone companies, when you phone them up to cancel, expect a hard sell tactic to keep you on.
Its much easier just to go Pay as You Go. Three do a mobile data sim that gives you 200mb per month free data, that can be used as a regular telephone sim card at the same time and charges 3p per minute, 2p per text, and 1p per mb of data.
All my phones use them and I have never felt the need to use anything else for about 5 years now.