They're some of the most popular mobile networks in the UK, but it appears that EE, Vodafone, O2, Three and giff gaff are all having issues this morning.
According to Down Detector, the issues at EE started at around 10:35 GMT, and are affecting users across the UK.
While the reason for the outage remains unclear, of those who reported issues, 65% reported problems with their mobile phone, 18% with mobile internet, and 16% couldn't access the mobile network.
Meanwhile, there also appears to be problems with O2, Vodafone, Three and giff gaff, also starting this morning.
Speaking to Mirror Online, a spokesperson for O2 said: "Today the industry experienced an issue that meant some calls between different networks were unable to connect. Specifically, O2, Vodafone and Three were unable to connect to EE and EE customers were unable to connect to O2, Vodafone and Three.
"At a time when the country needs connectivity most, it is important we work together rather than pointing fingers before facts have been determined.
"As this was a problem for a multiple networks, there is a National Emergency Alert for Telecommunications and Ofcom call at 2:30pm this afternoon to determine the route of the issue to ensure this doesn't happen again."
Many frustrated Brits have taken to Twitter to discuss today's outage.
One user tweeted: "Is EE down? I was in the middle of a call with my mother about half an hour ago, call cut and dropped, and now I can't get through to her. Just keep getting "call failed"."
Another added: "Is it just me or are the phone lines down? I suddenly can't make or receive calls."
And one joked: "I'm not into #conspiracytheory but with this #CoronavirusOutbreak and now phones down. Some s*** is going down."
The outage is a particular issue for the millions of Brits who have been advised to work from home amid the coronavirus outbreak.
One user tweeted: "Between the Covid, O2 signal being down and my Sky not working - working from home is going swimmingly. Losing the plot."
Another added: "Very very bad time for @O2 to go down all over when people are working from home or even people that need to call doctors etc that don’t have a landline ridiculous couldn’t of timed it better."
