Verizon today announced plans to roll out Voice over LTE support in the coming weeks, thus enabling subscribers to experience crisper and higher fidelity phone calls. In addition, subscribers will be able to take advantage of HD video calls, essentially Facetime a'la Verizon.
HD Voice and Video Calling work only when both people are in the Verizon 4G LTE coverage area and are using VoLTE-enabled smartphones from Verizon. The calling experience customers know today remains the same if one Verizon customer uses a VoLTE-enabled phone and the other doesn't, or if a customer with a Verizon smartphone calls a customer of another carrier or a landline phone.
Verizon hasn't yet announced which phones will be able to use the service once it finally launches, but we can only hope the iPhone is in the mix. Though Apple hasn't officially commented on the matter, it's believed that iOS 8 will come with support for VoLTE.
One thing to keep in mind is that if two users are engaged in a VoLTE phone call and one ventures out of LTE range and switches over to 3G, the call will drop entirely. As LTE becomes more prevalent this will of course become less of an issue, but today it's certainly something to be aware of.