ATT WiFi calling - International roaming

First off, there is no prepaid elite unlimited plan, Unlimited Elite is the name of a postpaid plan. Regardless, as long as your phone is in airplane mode, roaming is not possible and therefore roaming charges are not possible. There are no roaming charges when on WiFi calling. Just be aware that if you call a local Irish number, you will pay international long distance rates. Being on WiFi calling is the same as if your phone was in the US.

@Daimieo Wi-Fi calling is restricted in the following countries as noted Vietnam is one of the countries. You can only use the International Day Pass or Pay Per Use rates. 

Excerpt for the link below. 

Wi-Fi Calling is restricted in the following countries: China, Saudi Arabia, India, Turkey, Israel, United Arab Emirates, Vietnam, Pakistan, Cuba, Iran, North Korea, Sudan, and Syria.

https://www.att.com/features/wifi-calling/

I did Wifi calling in Vietnam, and ATT charge the crap out of me when I was using Wifi Calling. It make zero sense. Why was there no warning? I even turn off my International Roaming, so that should have never happened yet it did. 330 dollar? (Edited per community guidelines)!

@Daimieo

Wi-Fi calling does not work in Vietnam because Vietnam prohibits it along with a handful of other countries that prohibit Wi-Fi calling. So it's not possible for you to have made Wi-Fi calls. You would have had to use cellular calling.

Turning off roaming only affects your data it is not affect your ability to make and receive phone calls or text messages.

https://www.travelerswifi.com/blog/all-you-need-to-know-about-wifi-calling/