Mobile phone network EE said its services are back to normal after a signal problem affected some of its 27 million customers last night.
The technical issue stopped some users from making phone calls, sending text messages or using the internet for several hours.
A company spokesman said that the problem had affected a small number of customers that was in "single digits" in percentage terms.
He said: "Last night's technical issue that caused a small proportion of our customers to experience problems with their signal has been resolved and all customers are now receiving a normal service.
"We apologise for the inconvenience caused to those customers affected."
Any customers still having a problem should be able to clear their phones by turning them off and then back on again, he added.
A tweet last night by the company, which also operates under the T Mobile and Orange brands, said they were aware of "Gremlins in the system".
Twitter users took to the social network site to voice their anger at the problem.
Richard Antwi said: "Customer service @EE getting it so wrong with the humour. what is there to laugh about when the service has been down for 2 hours?"
Megan Kelly said: "Must be on at least 6 hours without signal now? Sort it out @EE."
The problems come a week after EE was named the best network provider in the UK by consumers.
The report by network analysts RootMetrics found that the major networks provided "hugely varying" levels of service across the UK, with EE winning or tying for first place in every category.