UPDATE: O2 has posted this message on its Twitter account
"Data update: We've identified the fault and vast majority of people are back online. We're restoring access for the remaining ASAP."
Yesterday, the mobile phone network used micro blogging service Twitter to warn its customers that it was having problems with providing web access and MMS functions. It is thought the outage affected hundreds of thousands of UK monthly contract users.
O2, which holds an exclusive deal with Apple to offer the iPhone 3G and 3GS in the UK, said it was investigating the issue and would continue to restore service to those customers still without internet access and MMS functions. The network also said that PAYG customers and those with BlackBerry handsets owners not affected by the outage.
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See also: O2 launches hunt for best iPhone app