I'm implementing a fully libre open-source vowifi/volte client for Android that runs in JVM sandbox, rather than untrustable modem. During my development I went through a protocol detail that I was too lazy to implement: you're supposed to announce which is the last 4g cell you saw even when doing Vowifi. I just hardcoded a value and forgot about it.

And then, I get a user who tells me that their carrier is saying they are roaming, even though they don't. I'm a tad clueless at first, because they are the network, they ought to know (this even happen over VoLTE). I send them an updated implementation that reports the correct cell. And then they receive a "welcome back" SMS.

Anyway, it's possible that your carrier can do abroad vowifi, you just need your vowifi client to lie as to where it is.