[Update: It seems the O2 network outage is linked to global problems with Ericsson software. The Swedish company told the BBC that it was "aware of an issue and is investigating." We will continue to update this story as more information becomes available and the original story follows below.]
O2 customers across the UK have been hit by a network outage that has left them unable to use 4G and data services, meaning they can't access the internet without a Wi-Fi connection.
Some users have also reported problems with making voice calls, despite claims from O2 that voice services are unaffected.
The issue has affected an estimated 32 million people, as O2 also provides services for Sky, Tesco, Lycamobile, and Giffgaff mobile networks.
The problems were first reported at around 5:30am, with many users taking to Twitter to vent their frustration.
O2 issued the following statement on its website: "Our technical teams are investigating reports of issues when using data. Voice calls are working OK. Our technical teams are investigating."
However, some users are reporting that they're also unable to make voice calls or send text messages, so the full scope of the problem is unclear at present.
The network outage has also affected Transport For London, which uses the O2 network for its electronic timetable displays at bus stops.
That could make commuting across the capital particularly difficult with users of the O2 network unable to use 4G to plan their routes, and bus stop displays out of order.
If you are commuting this morning, it may be worth checking your journey before you leave the house – and don't expect to be able to send GIFS to your mates while you're on the train.