Normally, when Apple launches a new iPhone we U.S, it only sells models linked to operators. For a long time, however, customers can simply enter the store and choose to buy these devices at a “full price” (“Full price”). Thus, even if the device comes with the operator's chip, it is completely unlocked.
Shortly thereafter, however, Apple always starts selling the SIM-free. This option is nothing more than a model totally disconnected from operators, bringing in its box even that SIM card ejection tool.
Interestingly, in the iPhone XS, Apple offered this model already at launch, along with options linked to the four largest operators in the country (AT&T, T-Mobile, Verizon and Sprint). This did not happen with the iPhone XR, which until now was sold only with chips from such operators; now, that has changed.
Whoever enters a Ma store or purchases the device online can now opt for the SIM-free. It is good to make it clear that, this year, there is absolutely nothing different about these models other than the fact that they come without an operator chip and with the SIM card ejection tool. We are talking about the same models (A1920, A1921 and A1984 XS, XS Max and XR, respectively), which * do * have support band 28 (700MHz APT) in Brazil, Apple sells the models A2097, A2101 and A2105, as we already informed.
To summarize: in practice, it makes no difference to choose the AT&T, T-Mobile, Verizon, Sprint models as long as paying the “full price”, without any link with such operators or SIM-free. The only thing that changes, as we said, is the inclusion of the chip ejection tool and the absence of the operator's chip in the tray. 😉