I am one of the people that has to upgrade his 3G phone by 2020.  I want the cheapest decent smartphone I can get, including phones that are several years old.  Determining 4G compatibility is easy, but determining VoLTE isn't (most just list it as LTE).  Would it be too much trouble for Verizon to provide a list of compatible phones?  This is a giant pain in the derrière.