EE has apologised after a fault left some of its customers unable to use the internet on their mobile devices.
The UK network said only a small proportion of its 30 million subscribers had been affected.
The Down Detector site indicated the problem peaked on Tuesday afternoon, with customers in different parts of the country reporting issues.
EE said the problem had now been fixed. About 1,000 subscribers contacted the company to complain.
Many more may have been affected, but not everyone would have noticed the issue.
"Data services were affected for a small number of customers after one of our data centres experienced a power cut yesterday afternoon caused by a third party," said a spokesman.
"We immediately re-routed traffic to minimise disruption, and service was restored within a few hours.
"If any customers are still experiencing connection issues, they should switch their device off and on, or enable and disable Airplane Mode to resolve the issue.
"We apologise for any inconvenience caused."