A top Verizon (NYSE: VZ) executive said that the company's VoLTE interoperability testing with competitor AT&T Mobility (NYSE: T) is going well and that the company expects VoLTE interoperability with AT&T to be commercially available this year. The companies had previously said interoperability would be available by the end of last year.

Speaking at the FierceWireless luncheon panel on the Path to 5G last week, Adam Koeppe, vice president of network planning and technology at Verizon, said that the VoLTE interoperability trials between the two companies were progressing nicely. Koeppe was using VoLTE as an example of how the two operators have come together to work on interoperability and will likely be able to work together in other areas in the future, like 5G.

Likewise, in a December 2015 blog post, Bill Smith, president of AT&T Network Operations, said that AT&T had successfully achieved the first VoLTE exchange between AT&T customers and Verizon customers in limited, select areas.

Koeppe's comments are notable considering the two companies announced in late 2014 that they expected to have VoLTE-to-VoLTE calling between the two networks commercially available in 2015. At the time, Verizon said that engineers from both companies were doing extensive lab testing and were then going to move on to field trials. The goal of the testing was to allow customers to make seamless VoLTE HD calls between the two networks and lay the foundation for other Rich Communication Services (RCS) such as video calls, rich messaging and more.

Currently, Verizon customers can only make VoLTE calls if they have a VoLTE-enabled smartphone and are calling another Verizon customer with a VoLTE-enabled smartphone. Likewise AT&T customers with VoLTE-enabled smartphones can only make VoLTE calls with another AT&T customer with a VoLTE-enabled smartphone.

At the time of the 2014 announcement, both AT&T and Verizon said they were working closely with the GSMA on the interoperability push. The GSMA's Network 2020 program was designed to encourage carriers to speed up the deployment of IP communication services such as voice and video calling over LTE as well as RCS.

In November of last year, AT&T announced it had launched advanced messaging and video call capabilities using RCS. Advanced messaging allows customers to send larger files by text and know when the messages are delivered and read. With video call capability, customers can make and receive HD voice calls combined with real-time video. But to use either service both the customer and the person on the other end must be AT&T wireless customers with capable devices and within AT&T's coverage area. To do the video calling, the customers must both have video call-capable devices.

Related articles:

Verizon, AT&T to launch VoLTE-to-VoLTE calling interoperability in 2015

Report: Verizon, AT&T and T-Mobile show significant voice quality improvements in test of VoLTE networks

AT&T launches new capabilities using RCS, but interoperability remains up in the air