Affected phones, which may be every single O2 device, simply fail to show any kind of data connection and will not connect even when turned off and back on or when other workarounds are tried, according to users experiencing the problems.
"Our technical teams are working with their teams to ensure this is fixed as quickly as possible".
Outages were reported across the United Kingdom, including Manchester, London and Exeter.
"Voice calls are working OK. we are sorry for any inconvenience".
(DPA/PA Images/Getty)Why is O2 not working?
O2, which also provides data services for customers of Tesco Mobile, Sky Mobile and GiffGaff, said that the outage, which started at about 5.30am, was the result of a problem at a third-party supplier.