Not only were O2 customers affected by the outage but Giffgaff and Lycamobile customers, both subsidiaries of O2, are also stuck in a state of no service.
The O2 network has been hit by a technical problem so customers across the United Kingdom are unable to use 4G. Work is now ongoing to fix the fault and customers are being encouraged to use wi-fi where possible.
The outage is thought to be affecting about 32 million in the UK.
"One of our 3rd party suppliers has identified a software issue in their system".
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"As a result of this incident, we are experiencing a high demand on our network which means some customers may have issues making and receiving voice calls". They're now working hard to resolve the issue so we would imagine it won't be too long before its back up.
The outage caused "panic" and was described as a "glitch" by The Times newspaper, which reports the outage had a severe impact on the early morning commute in London, which relies on connected data for several transport systems. "This issue is being investigated".
O2 says it is trying to resolve the issue as fast as possible.
The issue has left many customers inconvenienced.
The company, the second-largest mobile network in the United Kingdom, said it was investigating the technical fault. Some voice calls are getting through but all 4G and SMS services are completely jiggered.