Im my case, it's T-Mobile USA postpaid + DTAC prepaid, so no travel eSIMs.

Apple says DTAC supports their direct transfer mechanism (and I know T-Mobile does, since I've done it). What I don't know is whether a direct transfer is possible for a given eSIM when not on that eSIM's native network. So if I try to set it up a new iPhone in the USA, I don't know if I can get the DTAC eSIM transferred properly. And if I try to set it up in Thailand, I don't know whether I can get the T-Mobile eSIM transferred properly.

And if I can't get the DTAC prepaid eSIM transferred to the new phone, I don't know if there's even a way I can keep my Thailand phone number at all. I do have the original QR code card when I bought the eSIM but I'm not clear it can be reused or even used as evidence at a DTAC shop to 'reclaim' the number.

Feels like for this scenario I might be able to reduce risk by converting the DTAC prepaid to a postpaid account. At least then the phone number is more directly associated with *me*, and there should be a straightforward way of working with DTAC to get that number transferred into an eSIM on a new phone.