Here's a copy of a post I made on MacRumors regarding the esim/WiFi simulation. BTW, calls made this way register on my account log as "WiFi Call" just like one actually made over WiFi.

I've got a new question that occurs to me. If I am roaming overseas and have my iPhone set to the simulated Wifi service over a data line, will I be able to call another iPhone set the same way that is also roaming internationally? Both phones have US numbers and the same configuration. Phone one would dial phone two's US number with a +1 prefix. Would both phones connect using the simulated WiFi connection for no charges? It seems like it should work.

I'm hoping someone will be able to try and make a round trip call using the IMS configuration so I don't have to wait until March to test it.