Verizon and AT&T said today the companies are taking the next step in the evolution of VoLTE (voice over LTE) technology by enabling VoLTE- to-VoLTE connections between Verizon Wireless and AT&T customers. VoLTE interoperability between Verizon and AT&T customers is expected in 2015.

VoLTE is an all-IP (Internet Protocol) technology that deeply integrates the network’s enhanced calling features into the smartphone, creating a seamless and simple experience for customers. Interoperability among VoLTE service providers in the United States and around the world will create a better and richer mobile experience for customers.

Engineers from both companies are working through a full set of requirements, beginning with extensive testing in lab environments and then moving to field trials. This approach ensures customers will have a seamless experience making VoLTE HD Voice calls between networks and lays the foundation for interoperability of other Rich Communications Services (RCS) such as video calls, rich messaging, and more in the future.

“Customers use their smartphones to connect with friends, family and colleagues across service providers and around the world. Interoperability among all VoLTE providers takes connectivity to the next level with HD quality voice and additional features that customers want,” said Tony Melone, chief technology officer at Verizon. “We’re pleased to be working with AT&T as our first interoperating carrier, and we look forward to working with other operators as VoLTE continues to grow.”

“Interoperability of VoLTE between wireless carriers is crucial to a positive customer experience,” said Krish Prabhu, president, AT&T Labs and Chief Technology Officer, AT&T. “Customers expect to be able to connect anywhere, anytime– and as LTE technology continues to evolve, it’s imperative that we provide a seamless experience between carriers. We are pleased to work with Verizon on this initiative. We continue to work with others in the industry on similar collaborative arrangements and hope to see similar collaboration across the industry in the near future.”

Verizon introduced its Advanced Calling 1.0 services across the United States in September, and will continue to make Advanced Calling-capable smartphones available to its customers, further expanding the reach of the technology.

AT&T introduced VoLTE services in its initial markets earlier this year, and will continue to expand to more devices and more markets across the United States.

AT&T and Verizon Wireless have worked closely with the GSMA on this initiative. The GSMA’s Network 2020 program is designed to encourage mobile operators globally to accelerate the adoption of native IP Communication Services such as voice and video calling over LTE as well as Rich Communications Services (RCS).

“Customers benefit even more when services are interconnected and this will extend the reach of rich and reliable all-IP communications to a customer’s contacts on another network,” said Alex Sinclair, Chief Technology Officer, GSMA. “Embracing an all-IP future is vital for operators worldwide and the GSMA is delighted that AT&T and Verizon Wireless are bringing these services to their customers.”