As many as 3.2 million Vodafone users may have been unable to make calls due to a UK-wide network outage.
Internet forums and social networking sites are flooded with complaints after users have been unable to use Vodafone's network for calls and text messaging.
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In a Vodafone internet forum a Vodafone employee wrote, "There is currently a network server issue which is effecting customers all over the UK, our engineers are aware and are currently working on it as a high priority."
A Vodafone spokesman said, "We had a break-in last night at one of our technical facilities which resulted in damage done to some of our equipment. This means that some customers may be experiencing temporary loss of voice, SMS and internet services."
"We are working quickly to restore these and will be back to normal as soon as we can. There has been no impact on the privacy of customers' data."
According reports on Twitter, the network has been down since the early hours of the morning. Some internet reports suggest millions of users have been affected after a problem at a datacentre based in Basingstoke.