O2 investigating network data problems
Thousands of O2 customers in the UK have reported problems using data and 4G services.
Many users took to Twitter to complain about the difficulties, which were first reported at about 05:30.
An O2 spokesperson confirmed the problems, saying: "Our technical teams are investigating reports of issues when using data."
The spokesperson added: "Voice calls are working OK. We apologise for any inconvenience."