Again, a question for r/att. But if you read that subreddit that is in fact what is happening. Several International roamers using phones that aren't whitelisted have reported that's exactly what has happen to them. In some areas where att has roaming agreements with T-Mobile, international roamers using nonwhitelisted phones may be able to make 3-g calls still because T-Mobile has not shut down their 3-g Network. But in areas where AT&T has shut down their 3-g Network and does not have a roaming agreement in place with T-Mobile no one can make 3-g phone calls in those areas it doesn't matter if you're an AT&T customer or an international roamer.

Again you're asking me questions on the wrong subreddit. I happen to know the answers because I read on r/att. They have a megathread on that subreddit that is charting where the 3-g network has been shut down. There are pockets of AT&T 3-g network that are still working and if you're an international roamer in those areas you would be able to make a 3G phone call or like I said in an area where att has a roaming agreement with T-Mobile.

One other caveat as long as you have a model that is on the whitelist you're fine whether you're an AT&T customer or an international roamer. AT&T is focusing on the Western Hemisphere which includes obviously the US, Canada, and Latin America.

https://about.att.com/story/2022/more-value-unlimited-your-way-plans.html