O2's phone and data network services, which have suffered outages since lunchtime yesterday, are gradually get back to normal, according to the company.
"We can confirm that our 2G network service has now been restored," said O2 in a statement. "Customers who were affected should now be able to make and receive calls. Our 3G service is starting to restore and customers should expect to see a gradual return of data services as the day progresses."
O2 advises customers still experiencing problems with their handsets to "turn it off and on again", as rebooting will help handsets interface with the restored service.
"We are sorry again for the inconvenience this has caused and can provide reassurance that we continue to deploy all possible resources and will do so until full service is restored," said O2.
The operator was unable to provide Computing with further comment regarding the cause or exact nature of the network outages.
Michael Allen, director of IT service management at technology performance company Compuware, compared O2's problems with the recent NatWest and RBS breakdowns, arguing that such problems are often the result of fragmented systems management.
"Too often institutions are managing the technology stack in silos," he said. "The problem is, the systems that make up these day-to-day services are getting more and more complex and interdependent. O2's ability to deliver a service to customers will rely on hundreds of different components, systems and applications working in harmony.
"This can make preventing these types of service disruptions difficult as well as finding the root cause time consuming. This is why a new approach needs to be taken; companies must manage their technology services in a much more integrated and holistic service-centric manner."
Steven Hartley, telecoms practice leader at analysis firm Ovum, said the outages reflected badly on UK telecoms companies, particularly in the run-up to the Olympics.
"The huge influx of visitors to London ahead of the games will cause network traffic spikes, putting pressure on the UK's mobile networks, which already have a poor reputation compared to others in Western Europe," said Hartley.
"While UK mobile operators claim to be prepared, they have not yet given indication of the scale of their plans."
Hartley said mobile capacity upgrades in "crowd hotspots" would undoubtedly take place before the Games, but on occasions when large crowds pass through less well-prepared signal areas, network overburden could "prove disastrous".