This is why VoLTE is so important for operators ...
This is a video of Gabriel Brown, of Heavy Reading, giving an excellent five-minute primer on Voice over LTE (VoLTE), both on its short-term rollout and its long-term potential as the core of future connectivity networks.
One quote that sums up why VoLTE is so important:
Voice is a critical application, with a lot of revenue. People pick up the phone and want to make calls and want it to work. That's why then need it.