I understand, the person above says they have a non-VoLTE phone, which will make voice calls on 2G or 3G.

there’s something called CSFB (circuit switch fallback) which allows you to make old school voice calls/sms without using IMS (volte) over 4g network

My understanding is that CSFB works by signalling the LTE/4G handset to handover to the 3G or 2G network and continue the call setup on there. If carriers have shut down their 2G and 3G networks then there is nothing providing Circuit Switched services to fall back to.

Yes it’s def how it worked on the “backend” but i don’t remember what it did on the channel layer tbh. Maybe there’s a compatibility mode in enodeb. Also all three major providers have def shutdown their 2g/3g equipment as of last year