4G stands for fourth generation of mobile network technology, whereas LTE stands for Long Term Evolution. When 4G was first introduced it proposed a drastic improvement over 3G, however, was unable to meet the mandated specifications. Thus, the term LTE came into existence, which was kind of a middle ground standard between 3g and 4g technologies. Hence, LTE is not a technology, but the path followed to achieve 4g.
Today Vi offers VoLTE, short for Voice over LTE, which is an advanced technology for high-quality sound over voice calls. Read more about Vi VoLTE here!