My American number has been on Google Voice since 2015, and the rest of the world uses messaging apps so when I travel I've never used "backup calling".

It looks like only the S-series Samsung phones can have the extra bands unlocked--it definitely doesn't work on the gigantic M-series phablet that I use for motorcycle navigation.

I ended up ordering a Pixel 8a from Amazon US with the $100 gift card promo. Once Google gets find my device rolled out completely, that should be a nice plus too--AirTags aren't as useful in places where Apple only sells 5-10% of the phones in people's pockets.