EE has confirmed it is experiencing technical problems with mobile signal, leaving some customers nationwide unable to make phone calls to landlines.
The telecoms firm has said it is working to fix the issue and told one user who contacted the company on Twitter that the problem was "priority one" for them.
EE told another Twitter user that they were working to resolve the issue "as soon as possible."
The company also said that the signal problems were only affecting calls made from mobile phones to landlines - calling it a "severe outage" - though some EE customers on Twitter were reporting more widespread issues regarding complete signal loss.
Users of other mobile networks, including O2, were also reporting some connection issues via social media.
In a tweet, EE said: "We're aware customers from EE and other networks are having issues calling landlines. We're looking into why and we'll keep you posted."
In a statement on their Live Status Checker webpage, O2 confirmed BT was investigating an issue with its network.
"We are aware of an issue where some O2 customers may be experiencing difficulties making calls from their mobile to EE mobiles and to landline numbers," the firm said.
"BT, our fixed line partner, have confirmed they are investigating a problem within their network and we apologise for any inconvenience."