O2, the phone network, has broken across the UK. The carrier has been hit by a major outage, according to the monitoring site Down Detector. It is also affecting other companies that uses O2's network, such as Giffgaff. Problems include failure to access data, make or receive calls or send text messages, according to users on Twitter. But it does not appear to be affecting all O2 users, and it is not clear how some people are still able to use their phones.