The nation's two largest mobile network operators have begun to commercially deploy interoperable Voice over LTE (VoLTE). Finally.

VoLTE offers as much as three times more voice and data capacity than 3G technologies, enabling higher quality connections. The technology also allows carriers to increase bandwidth.

AT&T (NYSE: T) confirmed to FierceWireless that some of its customers can now place VoLTE calls to Verizon (NYSE: VZ) users. Verizon declined to comment, however.

"Currently, we are working with Verizon to allow our customers to enjoy that clear audio quality and video calling features when placing VoLTE calls to Verizon customers and vice versa," an AT&T spokesperson said. "In December, we saw the first VoLTE exchange between our customers and Verizon's in limited, select areas. We're working with others on this same feature, too."

The news follows several Reddit posts last week claiming the carriers had begun to support interoperable HD voice in some markets.

A top Verizon executive said earlier this year that the company's VoLTE interoperability testing with competitor AT&T Mobility was going well and that he expected 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, but they fell short of that goal.

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

T-Mobile said in May that 52 percent of its voice calls were routed on VoLTE, although the operator didn't discuss interoperability with other service providers. "When you look at the amount of spectrum that is being dedicated to 4G LTE, it's only 52 percent of our spectrum," CFO Braxton Carter said at an investors conference in May. "We're actually very aggressively refarming first PCS spectrum, then we'll go in and start refarming increasing amounts over time, so we have amazing capacity in a very spectrum-differentiated standpoint."

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