Mobile operator O2 claims to have fixed network problems that left hundreds of thousands of customers without voice and data connections for around 24 hours.
"Following previous updates, our tests now show that all our 2G and 3G services have been fully restored for affected customers," the company said in a statement.
"If any customers are still having problems we recommend they turn their phone off and on again. Once again, we are sorry."
O2 customers began experiencing problems with their voice and data services on Wednesday afternoon. Subscribers to GiffGaff and Tesco Mobile, which piggyback onto O2's network were also affected.
O2 told Techworld's sister site Computerworld UK that the problem lay with one of its network systems, which was having difficulty registering mobile numbers on the network.
O2's UK Twitter account was inundated with abusive complaints, some of which solicited amusing responses.
For example, the following tweet from O2 customer Johny Huntz: "@O2 your mum gave me a better service than you s**t c***s," was met with: "@Johnhunterr Afraid she said different about you. But the signal's up and running again now, yay."
O2 later used its Twitter account to announce that it was still working to identify the root cause of the incident, and was keen to restore confidence and trust.
"For those customers affected by the lack of service, we will be doing everything we can to make it up to them in an O2 way," it added.
However, some industry commentators have suggested that the service failure could have long-term repercussions for the company.
"To have an entire network down is a poor show for the company, and does not bode well for an operator who plans to deliver 4G services in a year's time," said Askar Sheibani, CEO of IT and telecoms repair company Comtek.