Millions of customers have been unable to access their data on the O2 network after the company experienced technical problems.
Here is a selection of some of the difficulties people have experienced when they were unable to use the service.
Emergency in central London
Peter Wilson, from West Drayton, realised the importance of mobile technology when his partner collapsed in central London.
"Libby collapsed in the branch of a well-known coffee chain when she was on her way to work," Peter told the BBC.
The couple were eventually able to make contact via wi-fi and the emergency 999 number.
Thankfully, Libby is now recovering but he says: "It made this morning very stressful and at a critical moment it provided clear evidence about how reliant we are on data and phone networks."
Off the road
Greg Ashworth, a senior insurance clerk in Blackpool, received a notification in the morning telling him there was no service on his network.
To make matters worse, Greg told the BBC his motorbike also broke down on his way to work.
Not only was he unable to phone his employer to say he was running late, he could not get through to the breakdown company.
There was a limited service later on so he was eventually able to contact his manager and a taxi firm.
"The downside was I've had to abandon my motorbike."
Unable to access rotas
Lynsey Greaves, who works for a domiciliary care agency in Doncaster, where electronic care monitoring is used, told the BBC carers were unable to see their rotas because of the outage.
They were also unable to log in to service users' calls, see maps or send messages.
"It brought our company to a halt. Nightmare. What was their plan B?"
By Bernadette McCague, UGC and Social News