Millions of smartphone users in the UK have lost their data services after the O2 network suffered technical problems.
O2 has 25 million customers, but also provides services for the Sky, Tesco, Giffgaff and Lycamobile networks which have another seven million users.
O2 blamed the problem on a supplier and Ericsson, which makes mobile network equipment, said it was working to solve the issue.
Japan's Y!Mobile network, owned by Softbank, also suffered big problems.
O2 said: "We believe other mobile operators around the world are also affected. Our technical teams are working with their teams to ensure this is fixed as quickly as possible.
"We'd encourage our customers to use wi-fi wherever they can and we apologise for the inconvenience caused."
The difficulties in the UK were first reported at about 05:30 on Thursday.
Spain's Telefonica owns O2, which has the UK's second-largest mobile network after EE, which is now part of BT.
The company has said voice calls are not affected by the problem, but some O2 customers say they cannot make calls or send texts either.
The outage is having knock-on effects for other services that use the O2 network, including Transport for London's electronic timetable service at bus stops, which has stopped working.
Other Japanese networks using Y!Mobile's infrastructure have also been affected. The firm apologised for the inconvenience caused.
One O2 customers, Allison Rose-Mannall, from Norwich, is an insulin-dependent diabetic who relies on her mobile and is unable to get to a landline.
"I'm disabled … I'm in a wheelchair," she told the BBC. "So having no data but also no calls as well means I can't contact anyone if I have a fall or if I need anything."
Lynsey Greaves runs a company in Doncaster providing home visits to the elderly and vulnerable. Her 130 staff all rely on O2 phones to access rotas, schedules, names and addresses. Since 530am she's been calling in extra office staff to give out the information for each visit over the phone.
"There are nine of us trying to sort it now," she said. "It's been a nightmare."
Luke Stagg is trying to run a plumbing business via his phone, but he can't get through to customers or use his sat nav.
"That's a whole day wasted," he says. "I'll be seeking to recoup my losses, especially as a business customer."
But a few people have actually welcomed the forced screen-break.
"Remember the not so distant past, when people weren't wandering around like zombies, glued to social media?" says O2 customer David Flanders. "Remember striking up a chat with the stranger next to you on the train or the bus?
"I am certainly not going to lose any sleep over losing my data for a while."
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