Thousands of customers of the Three mobile network were left unable to use their phones last night after a massive blackout.
The network went down across many parts of Northern Ireland at around 6pm for over three hours.
Customers reported problems in Belfast, Bangor, Downpatrick, Ballyclare, Bushmills, Larne and Randalstown.
One user who contacted Three customer services said: "I'm very annoyed but they have agreed to a credit on my bill for the inconvenience. They warned that there was an issue with the update for 4G and that engineers were working on it and it should be resolved within 24 hours. It came back about half nine, so I was affected for about four hours in total."
A spokesman for Three apologised for the inconvenience but denied the blackout was related to a system upgrade.
"We're aware some customers in Northern Ireland have experienced issues with their service this evening. Service has now been restored. We apologise for the inconvenience caused to affected customers," he said.