Telefónica claims it is the first network operator to be able to transfer voice calls from a LTE '4G' network to a 3G network, using equipment from various suppliers, without interruption.

This means that callers on a 4G contract can move between 4G and 3G networks without their calls dropping out.

Telecommunications equipment vendors including Huawei, T-Mobile Austria and Qualcomm have already succeeded in handing calls over LTE to 3G networks, using only their own equipment. However, Telefónica says it is the first to do so using multiple handsets and components from several different suppliers – corresponding to actual conditions in today's mobile communications networks.

In a statement on Thursday, Telefónica said the handover was achieved in a testing laboratory in Germany. It will demonstrate the new LTE-to-3G capabiltiies at the Mobile World Congress conference later this month.

"Telefónica has achieved a significant landmark with the successful testing of this mobile broadband network for the future,” said Enrique Blanco, CTO of Telefónica.

Blanco added that using voice services over LTE networks (VoLTE) would enable an improved experience on mobile devices. "With VoLTE, our customers will be seamlessly connected to a superfast intelligent network that not only gives a top quality voice service – but also a network that opens up a new world of opportunities, such as high definition video calls."