O2 boss Ronan Dunne says 'sorry' to customers
12 July 2012 Last updated at 18:16 BST
O2 says it has fixed network problems that left hundreds of thousands of customers without voice and data connections.
"Our tests now show that all our 2G and 3G services have been fully restored for affected customers," the firm said in a statement.
The news came about 25 hours after O2 said the problems first emerged.
Ronan Dunne, Chief Executive of O2, has apologised to customers for the disruption.