02 told customers with smartphones to turn off their 3G data to allow them to make calls and send text messages as it gradually restored its service today.
Hundreds of thousands of customers facing a second day of disruption have found they are able to make calls and send texts if they turn off 3G mobile data.
An 02 spokesman confirmed that it was encouraging those with smartphones to turn off their 3G capability to regain basic service, saying that its 2G network had been restored.
The spokesman said 3G was “starting to restore” but he could not give a timeframe for when customers could expect to see the entire service back to normal.
“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.”
Engineers worked through the night to fix the fault after network problems started to be reported early yesterday afternoon.
A company spokeswoman said earlier: “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
“We, and our central supplier, have deployed all possible resources and have been working through the night to restore service as soon as possible.”
The spokeswoman said it was unclear exactly how many have been affected by the nationwide problem, but estimated it was “thousands” at least.
Many disgruntled customers took to Twitter this morning to vent their frustration at still being unable to use their phones.
Sean Foster (@SeanFoster) tweeted: “Arrrrrrrghhhhh! My phone was fine all day yesterday and now after their failed overnight work o2 have screwed it!!”
Another Twitter user Leanna May (@LeannaMai) said: “I can’t bare this any longer!! THREE @o2 contracts, NONE WORK. And I’m at home pregnant in agony! Great, who should I call? No one!!”
David de la Mere (@dmeeno) also took to the micro blogging site, tweeting: “I probably shouldn’t have been so smug about having an @O2 signal yesterday. I don’t have one now.”
Tesco, which uses O2’s masts for its Tesco Mobile network, confirmed that some of its customers were also being affected this morning.
O2, which was formed in 2001, following the demerger from British Telecom of its former mobile business, BT Wireless, is urging customers to check their Twitter and Facebook feeds for updates.