Or a spare used/old phone with eSIM capability?
/r/usmobile has a $10/mo plan that can be up and provisioned (usually in just a few minutes) as a second line.
kicker: as long as you’re physically in the US . But you can create an Apple ID with prepaid intl SIMs too.
I'm in the states, so that simplifies things.
they sell AT&T as “dark star” Verizon as “warp” T-Mobile as “light speed “
You pick when activating.