EE customers are currently having issues with phoning people through 4G throughout the UK. The issue was initially reported from London, however it seems like the issue is wide spread and is affecting customers everywhere in the country.
An EE Spokesperson commented on the issue on social media.
We’re aware that a small number of customers are unable to make some calls. We’re doing our best to fix this quickly. Please keep retrying, and we apologise for any inconvenience. WiFi calling, as well as text and data services, are not affected. - Beth— EE (@EE) May 21, 2019
Many customers have complained on social media and have reported the issue on Down Detector, with over 1000 reports at the time of writing.
The outage seems to be covering areas including London, Birmingham and Glasgow.
Customers can get round the outage by using Whatsapp Voice Calling instead of usual 4G calling. This works because 4G internet is still online.