The mobile operator Three has confirmed some users are currently unable to make phone calls.
In a post on X, the network said there was “an issue affecting voice services” but did not say how many of its 11 million customers are affected.
Outage website DownDetector reported a spike in issues at 09:30 BST on Wednesday, with over 9,000 reports made by users.
Data services such as 4G and 5G are working as normal, according to Three.
The company recently completed a merger with Vodafone to create the UK’s largest phone network with around 27 million customers.
Vodafone services are running as normal.
However, other phone companies which piggyback off Three’s network are affected.
ID Mobile posted on its service status page: “Please bear with us, our technical teams are working hard with our network partner Three UK to fix this issue and full service will be restored as soon as possible.”
Smarty said it was “aware of an issue affecting voice services” and was working to fix it.
Some customers have posted on social media saying they have been unable to return missed calls from the hospital, or to call a car breakdown service.
Others also said on Wednesday morning they did not have access to data services – though in a statement, Three has said data is “working normally”.
In January, Three announced an investigation into a small number of users not being able to call 999 during a network outage.