One of the big features touted for the future of the iPhone 6 and iPhone 6 Plus is support for Voice over LTE (VoLTE). Phone calls made over VoLTE are expected to not only have superior call quality, but some future capabilities like video phone calls and rich messaging depend on the technology. There’s only one problem — in the few markets where VoLTE is enabled at this time, users are only able to make phone calls to other individuals on the same carrier’s network.

Today, AT&T and Verizon pledged to allow interoperability of their VoLTE networks, making it possible for users to make VoLTE calls between the two networks. Verizon’s CTO, Tony Melone, said that the company will seek similar arrangements with other carriers as they begin VoLTE deployments.

AT&T has started VoLTE deployments in selected markets, while Verizon’s Advanced Calling 1.0 rolled out nationwide in the US in September. Verizon users need to add the services to their account through the carrier’s website, while VoLTE is immediately available to AT&T customers in supported markets.

It’s simple to enable VoLTE on an iPhone 6 or 6 Plus – just fire up Settings, then select Cellular > Enable LTE > Voice & Data. The interoperability between the AT&T and Verizon networks is expected to begin sometime in 2015, although the carriers did not say exactly when.