Can a website see my IMEI number? I have been banned from a website for multiple accounts, although I always cleared cookies, disconnected and reconnected from "the cloud" which gives me a different IP address every time. How do they know?
Cookies are not the only persistent mechanism they may be using. Flash LSO, HTML5's Local Storage are two that come to mind...
Did you really deleted all of your cookies? Google, facebook and every remote auth mechanisms enables to find out your indirect identity. For example, the stackexchange site are identifying me by asking google, who am I. And google identifies me by my session cookie to the google.
As an alternative solution, you could use tor, although it could be costly and inefficient on a gprs network. Maybe you need to build a tor proxy on a remote server.
Another solution were to make false evidence against both human (for example, assigning typical spellchecking errors of wellknown users) and automatized sockpuppet detection (for example, falsifying browser type, browser location data and X-Forwarded-For headers).