I bought the T-Mobile 128 GB version from Apple’s clearance section. Received it two days ago.
Phone is 100% unlocked and tested. I popped in my other foreign SIM card from AIS Mobile (a Thai carrier) and it works without a problem.
The only reason why they mention that the phone is “T-Mobile” is because it comes with a T-Mobile SIM card already installed.
Back in the day, it was different. On older generation iPhones, carrier branding meant that the phones themselves were physically carrier-branded with their logos.
Today it’s not like that. There is nothing “T-Mobile” about the T-Mobile iPhone SE. Only the SIM card, which is removable. If you pop in another GSM SIM card, that carrier will update and overwrite carrier settings on the phone automatically, since the phone is unlocked.
After that, there will literally be no trace of “T-Mobile” anywhere on the software or hardware. The box doesn’t reflect this either, which means that if you remove the T-Mobile SIM card, you can offload your phone as just an unlocked one without ever having to mention that it’s “T-Mobile”. That’s irrelevant.