The real secret is how many times your device connects to internet to check your mail,twitter and similiar applications because every time when it connects your mobile operator takes off from your account 100kb of data. Even if you have no new messages. But if you have application on your phone which keeping connection all the time your data consumption is about 80% smaller. I´m using Nokia Messaging from a few weeks and it keeps connection all day long so I observe that data consuption is very,very small.