The giant operator said on Twitter shortly before 8am that its services are back to normal, after customers - including some in Shropshire and the Black Country - reported problems throughout Wednesday afternoon and evening.
Some 15 hours after announcing there were problems with mobile services the company announced: "Our mobile services are back to normal. We're sorry for any inconvenience caused while we restored service."
According to Down Detector, a website that provides real-time information about the status of various websites and networks, the information seemed to verify the statement.
Down Detector said more than two-thirds of those reporting problems said they had a lack of mobile internet, while a fifth said they had no signal. Some users said they had total blackout, with no internet or signal.
Customers in Shropshire and Wolverhampton were complaining about the outage, while other locations affected included London, Birmingham, Manchester, Liverpool, Newcastle, Leeds, Glasgow and Edinburgh.