With over 25 million customers, O2 is one of the world's leading digital communications companies. They run 2G, 3G and 4G networks all over the UK and operate their own O2 Wifi. Shop on their website to see the latest tech gadgets, from Apple iPad to Samsung Galaxy, iPhone to Sim only. They also offer O2 Rewards. You can expect 5% -10% back on your payments, which you can use to buy extra credit, phones, accessories, shopping vouchers or Ticketmaster tickets.