but the calls will be on a different number, and anyone calling you will incur international charges, if from the US.
Yeah, that could be a big headache, if you get the more expensive esim which includes a European phone number. And as has been said here a lot, in 6 weeks, you might possibly need to contact a bank, credit card, or other business which needs to use 2FA to validate you. If that happens, the European phone number won't help.
If you enable wifi calling on your iphone, you should be able to use your "normal" AT&T phone number for 2FA and calling/texting friends back home, while you are connected to a hotel's wifi. That way, you could buy an inexpensive data-only esim for all the travel apps and web surfing you might want to do. AT&T might charge you a small amount per call/text for that, you'd have to read up on the details of your specific plan.
I'm an Android guy, and not so knowlegable about the Apple world, but I believe that recent iPhones can do sort of a "wifi calling" trick where they get data from the #2 esim, and can make calls/texts using the "normal" number on esim #1. I've tried to do this with my Android version 16 phone, and cannot do it.
Has anyone here been able to do that with an iPhone? And what iPhone o/s version was that with?