I don't know single phone top of my head that supports EU LTE bands and a single US carrier LTE bands. US has it really complicated as big carriers have cut some of the frequencies to different bands for separate carriers.
Anyways thinking on what SoC they have on Jolla LTE should not work over in US.

Do we know Jolla hasn't gone through FCC? I don't remember how it went back in the N93 etc days when plenty of American's did order their Nokia's from overseas. N95 at least had its US versions.