"We apologise for any inconvenience", the firm said, after problems were first reported at around 5.30am.
The network outage has also affected Transport For London, which uses the O2 network for its electronic timetable displays at bus stops.
TFL said: "The company that updates the data to our network of Countdown Systems is now experiencing difficulties in providing this service".
It doesn't end there, because some major MVNO (virtual networks) that piggyback O2 signals are experiencing the same disruption. But data connections are broken. Woke up this morning with no mobile data at all and I have turned mobile data off and also powered my device down and still no mobile data? Here is what business professionals and mobile users need to know about 5G networks. "Down? Really?! @O2 appalling coverage all the time anyway, can't wait to switch out my service provider".
Here's the full list of the 8 XFL cities and their venues
They are focusing on shorter games (less than 3 hours), changes to rules with changes to punts, extra points, and more. He said that their ideas for the league and their reimagined version of football are now being tested.
U.S. and NMI flags lowered to half-staff in honor of 41st president
The White House said a state funeral will be held on Wednesday at the National Cathedral in Washington. Later, the then US President Richard Nixon appointed Bush as the Ambassador to the United Nations.
What made Michelle Obama drop the S-word
Naturally, Michelle Obama also said that Meghan has a great opportunity to make a difference, given her position. And you feel a bit resentful about it. "I am not saying that there are no talented people out there".
Many have been unable to access the Internet after reporting issues with 4G and data services.
The company said one of their third party suppliers has identfied a software issue in their system. We believe other mobile operators around the world are also affected.
O2 said it will be sharing updates on its website when the service changes.
Ericsson, whose central user database caused O2's 2012 25-hour mega-outage, told The Reg: "We are aware of the issue and are working together with our customers to solve it as soon as possible". Work is now ongoing to fix the fault and customers are being encouraged to use wi-fi where possible.