Mobile phone networks EE and O2 have resolved a problem which left some customers unable to make voice calls to landlines.
Users of both networks reported problems on social media, with O2 saying partner firm BT was investigating a problem on its fixed line network.
An EE spokesman said: "Customers of a number of operators have experienced problems calling landlines for a short period. The issue has now been resolved."
The company earlier 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 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."