O2 today have been unable to tell me how many people are affected but the network has a total of 23 million users. And customers with Tesco and Giffgaff are also hit, because they use the O2 network. I asked for an interview - O2 so far has been unable to provide somebody. Let's look at their statements.
It is "a fault with one of our network systems"
Some mobile phone numbers are not registering"
"We expect full service this afternoon"
A lot of 3G phones will also work on 2G - but you may have to switch off the 3G for that to happen. It's worth a try.
O2 are saying try turning your phone off and then back on. Re-booting can help your phone reconnect with the restored service, they say.
Twitter just now is bristling with comments.
Captain of Manchester City Vincent Kompany said:
Children's TV presenter Ricky Boleto:
Lots of users like Shirleen Strachen who says: "raging, what a joke, paying for a service I'm not getting". Olympics fans, athletes and organisers will depend on mobiles - so this timing is especially bad.