Thousands of O2 mobile phone customers hit by network problems HUNDREDS of thousands of O2 customers were still unable to use their mobile phones this morning after the operator's network crashed. Engineers worked through the night to fix the fault but many mobile users are facing a second day of being unable to make or receive calls. The network's text messaging service is also affected by the fault, while customers have had issues accessing data services such as the internet. Network problems started to be reported early yesterday afternoon, but it not yet know how many of 02"s 23 million UK customers have been affected. A company spokeswoman said: "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. A message on O2"s Twitter feed read: "Our engineers are doing their level best to resolve the current network issue. Apologies for the inconvenience caused. A later update read: "As of 8am today, our 2G voice and data service has been restored. We're continuing to work on the 3G service. No timescale for the repairs has been given. 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. Tesco, which uses O2"s masts for its Tesco Mobile network, confirmed that some of its customers were being affected this morning. "We are currently seeing a problem on our network affecting some of our customers," a spokeswoman said. "There is an issue within part of O2"s core network that is preventing some mobile phones from successfully connecting. We're sorry about the inconvenience this may cause our customers, and O2 engineers are dealing with the problem to restore full service as soon as possible.