It's likely that MVNOs that use EE signal are affected as well, which explains why our Production Editor (who is on EE) was able to call a Virgin number a short time ago.
Users across the country have reported being unable to make or receive phone calls to some numbers from their mobile phones. All data and messaging services are working as normal.
According to monitoring site Down Detector, the problem first emerged around 8am this morning.
The service provider has apologised for the problems on social media, and says it is "working to fix this as quickly as possible". However, it seems to be affecting only some calls to non-EE numbers. The signs point to customers in London and the South East sustaining the bulk of the problem, but there have also been reports of outages in Bristol, Birmingham and Nottingham.
CEO Marc Allera took to Twitter last night to say full service had been restored, adding: "I know that this has made the day very hard for some of our customers, and for that I'd like to sincerely apologise".
More than 1,900 customers are complaining about the EE network problems each minute, DownDetector data shows.
DownDetector claims 41 per cent of those EE customers complaining about the outage have been left without a fixed internet connection.
According to CEO Marc Allera the problem stemmed from an error on the EE interconnect platform, which is responsible for moving calls around the network.
One EE customer tweeted the United Kingdom mobile carrier, stating: "not able to send text messages, calls aren't coming through from other networks - need some troubleshooting!"
Users had bombarded EE with angry tweets, demanding to know when their service would be restored. "This is unacceptable" another posted.