I recently purchased a new phone from ATT....model shown in title. I found out yesterday ATT no longer sells anything but an intl day pass for $10/day up to max of 10days, then no further daily charges within a billing period. ie, if you go across billing cycles as my trip will you pay a max of $100 each bill. YIKES! ATT used to have a great plan called Passport in which a month long trip to GB & France crossing billing periods in 2019 cost me $70. I have been researching here on the forum and it looks like I can go to T Mobile (Verizon intl plan is similar ATT.) or get an esim. I think my new phone is compatible for GSM and CDMA both and also for an esim. Does anyone here know if what I am saying about my new phone is correct? Can you suggest other options for me? Please don't say call ATT as I have just literally spent 2 days talking to their idiot customer service phone centers on another issue and haven't gotten a clear answer yet.
In basic function, your ATT phone will work fine with a foreign SIM.
But you must be sure the phone is unlocked. (If you're on any kind of payment plan for the phone it likely is not.)
I bought the phone unlocked at Best Buy.
Glad you know that.
I've got early-onset luditeness, so haven't figured out the esim, though I know my phone is capable of it. I buy local sims when I travel, physically swap them out, and use data via that.
You will need to confirm with AT&T that your phone is indeed unlocked - though you may have bought an unlocked phone, they may also have restrictions based on your plan or account balance. They're sneaky that way (I have AT&T). I am also annoyed they got rid of their passport plan, but what you described about their billing process I believe is correct. The only way I can think of possibly getting around it is changing your billing cycle so that it doesn't cross your travel period (but if you're leaving soon that might not work).
If your phone is truly unlocked, review the many recent posts about buying an eSim. Your phone is compatible with Google Fi, which is what I am investigating for my upcoming trip - much better pricing for international travel than AT&T. The recent posts highlight a lot of other options as well depending on where you're going.