VoLTE and SIP do indeed retail a lot of the concepts of circuit switched. The challenge is that now you have the complexity of (seemingly invariably) a Telco managing a k8s stack on an OS they don't understand, and which has hundreds of CVEs per month they aren't patching. The failure modes of VoLTE/SIP are also a load more complex than CS domain issues - IMS interop issues and XML parsing delights await!

So I guess it's not only about getting off the internet - there is a real shift in complexity in these more modern stacks too.