There is evidence that says it won’t work with US carriers. There is also evidence that it can support US carriers.
Librem5…
######### Librem5 ########################
purism@pureos:~$ mmcli -m 0
-----------------------------------
Bands | supported: pcs, g850, utran-4, utran-5, utran-2, eutran-2, eutran-3,
| eutran-4, eutran-5, eutran-12, eutran-13, eutran-17, eutran-25,
| eutran-26, eutran-41, eutran-66
And FLX1…
######### FLX1 ########################
root@FuriPhoneFLX1:~# mmcli -m 0
----------------------------------
Bands | supported: egsm, dcs, pcs, g850, g450, g480, g750, g380, g410, g710,
| g810, utran-1, utran-3, utran-4, utran-6, utran-5, utran-8,
| utran-9, utran-2, utran-7, utran-10, utran-11, utran-12, utran-13,
| utran-14, utran-19, utran-20, utran-21, utran-22, utran-25, utran-26,
| utran-32, eutran-1, eutran-2, eutran-3, eutran-4, eutran-5, eutran-6,
| eutran-7, eutran-8, eutran-9, eutran-10, eutran-11, eutran-12,
| eutran-13, eutran-14, eutran-17, eutran-18, eutran-19, eutran-20,
| eutran-21, eutran-22, eutran-23, eutran-24, eutran-25, eutran-26,
| eutran-27, eutran-28, eutran-29, eutran-30, eutran-31, eutran-32,
| eutran-33, eutran-34, eutran-35, eutran-36, eutran-37, eutran-38,
| eutran-39, eutran-40, eutran-41, eutran-42, eutran-43, eutran-44,
| eutran-45, eutran-46, eutran-47, eutran-48, eutran-49, eutran-50,
| eutran-51, eutran-52, eutran-53, eutran-54, eutran-55, eutran-56,
| eutran-57, eutran-58, eutran-59, eutran-60, eutran-61, eutran-62,
| eutran-63, eutran-64, eutran-65, eutran-66, eutran-67, eutran-68,
| eutran-69, eutran-70, eutran-71, eutran-85, ngran-1, ngran-2, ngran-3,
| ngran-5, ngran-7, ngran-8, ngran-12, ngran-13, ngran-14, ngran-18,
| ngran-20, ngran-25, ngran-26, ngran-28, ngran-29, ngran-30, ngran-34,
| ngran-38, ngran-39, ngran-40, ngran-41, ngran-48, ngran-50, ngran-51,
| ngran-53, ngran-65, ngran-66, ngran-70, ngran-71, ngran-74, ngran-75,
| ngran-76, ngran-77, ngran-78, ngran-79, ngran-80, ngran-81, ngran-82,
| ngran-83, ngran-84, ngran-86, ngran-89, ngran-90, ngran-91, ngran-92,
| ngran-93, ngran-94, ngran-95, ngran-257, ngran-258, ngran-260,
| ngran-261
The one that is winning at the moment is that it doesn’t support US bands… …because it isn’t working.