Comment by snazz

Yes, circuit switched fallback was possible for a time (LTE data and circuit-switched 2G or 3G voice). I think 3GPP shouldn't have written that into the spec in the first place, but you know what they say about hindsight....

The whole saga with VoLTE was really quite entertaining: https://nickvsnetworking.com/background-to-the-volte-mess/