EE has started switching on its next generation 4G+ network, which offers speeds of more than 400Mbps.
The network is being deployed in major cities across the UK and was switched on initially in Cardiff, where it achieved download speeds of 429Mbps.
EE's new technology has also been activated in London's Tech City area and will be rolled out in Birmingham, Manchester and Edinburgh later this year.
The provider believes customers connected to the sites will be able to "consistently experience" speeds above 50Mbps with the network, while peak speeds can exceed 400Mbps "with the right device".
EE's latest tests made use of the Xperia XZ Premium by Sony, which is one of the very few smartphones in the UK that supports Cat-16 technology and is optimised for the 4G+ network.
Marc Allera, Chief Executive of EE, commented: "Sony has raised the bar in smartphone speeds and we’re investing and innovating to match that and give our customers the fastest network speeds in the UK.
"What we’ve demonstrated live in Cardiff is more than ten times the average mobile download speed."
Mr Allera added that EE will continue expanding this new capability to the busiest parts of the UK.
This, he said, would ensure customers "always have a great connection to do the things they love".