00:00 12 July 2012
Thousands of O2 customers are falling victim to a "network systems fault" that has left them unable to make calls and send text messages.
A blackout struck the network on July 11th and, in its second day, the problems are still apparent but some users have discovered that they can send messages and make calls if they turn off 3G mobile data.
O2 recommended that switching to 2G is a temporary fix.
The mobile network issued a statement to their 23 million UK customers saying: "We can confirm that our 2G network service has now been restored.
"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.
"Customers affected may wish to try switching their mobile phones off and on as service returns. 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."
The problem started on Wednesday mid-afternoon and O2 have not yet issued a time-scale for when they hope to have all services restored.
It has also affected other providers who use 02's mobile masts including Tesco Mobile.
A service update revealed a little more about the issue: "We can confirm that the problem with our mobile service is due to a fault with one of our network systems, which has meant some mobile phone numbers are not registering correctly on our network.
"As a result, some customers are having difficulty making or receiving calls, sending texts or using data.
"We, and our central supplier, have deployed all possible resources and are working through the night to restore service as soon as possible. We apologise again to customers affected and will provide further updates as soon as we can"