(carrierexplode.com)
Apple/AT&T still haven't released any kind of statement addressing the issue other than to replace affected hardware.
A while ago I built a decoder for that (Qualcomm only!), it was fun and helped me improve the support of my device for my carrier.
A very common thing to do in Russia for instance where WiFi calling isn’t available: https://github.com/ios-bundles/CarrierSIM