I'd like to buy my mother, a T-Mobile customer, an iPhone 15 Plus. I've got a hefty amount of Best Buy gift cards that I was planning to use to pay for the phone, and have it activated on T-Mobile for her in-store.

Much to my dismay, Best Buy and T-Mobile cancelled their partnership the same day the new iPhones were announced. Now, the phone only appears to be sold through AT&T or Verizon activations.

I read online that non-Apple retailers sell Flex Lock iPhones, which are unlocked phones that end up locking to the first carrier the phone is activated on.

I used to be an employee a few years back, and if I remember correctly, scanning any phone's UPC in the point-of-sale system would give you multiple checkbox options, like 'UNACTIVATED UL' or carrier-specific options. If that's true, and the 'Flex Lock' thing is accurate, would it be possible to have an employee sell me an iPhone as an unlocked phone and then I could just personally activate said phone on T-Mobile?

I'm not entirely sure if the phones specifcally come boxed up for AT&T/Verizon or if they're all the same but just end up getting activated on those specific carriers.

Don't want to get anyone in trouble [if this isn't allowed], hence why I'm asking here instead of going in-store immediately. I'd really prefer to buy the phone at Best Buy due to the gift cards, but might ultimately end up just having to buy through Apple themselves. I reckon I'd end up using the gift cards on something eventually, but I've got nothing else in mind so I figured this would be an appropriate time to exhaust them.

Thanks for your time :)