Two of Verizon's rivals, AT&T and T-Mobile, have already launched their own VoLTE services, and T-Mobile's one already has a nationwide coverage. Big Red is also prepping to launch its HD voice call across the whole country, thus aiming for the lion's share of the VoLTE market in the USA.
In order to benefit from Verizon's HD voice service, one will have to sport a VoLTE-enabled device. Naturally, these are all smartphones that allow you to hook up to the carrier's 4G network. What's more, Big Red's VoLTE calls will be interoperable, so that users will be able to make clearer voice calls with any counter-opposed HD Voice-compatible AT&T, T-Mobile, or Sprint device. As sound logic suggests, this is pretty crucial for the future development and wider adoption of the nifty technology.
As roughly 80% of all the traffic on Verizon's network is an LTE one, the carrier is planning to release an LTE-only device sometime in 2016. This would only happen once all of Verizon's services make use of its LTE network, mind you.