If you're 18+ all you need to get your own phone sticker is a Passport or Driving Licence (Full or Provisional).
Take it to one of the following Post Office branches and as long as it is current, genuine and belonging to you then you'll get your sticker there and then. It takes around 5 mins and it's completely free if you get it before 1st November 2012.
Available at the following Post Office branches from - MONDAY 9TH JULY 2012