Beware that not all operators and SIMs work in all devices. A few yrs ago, was in CapeTown and the kiosk inside the airport selling SIMs insisted that I try it out. I had a new Nexus phone (always unlocked) at the time - it didn't work. A companion had a Galaxy which did, no issues.
In London, got a SIM for a few weeks there. The guy inside the O2 store took 5 minutes of changing settings to get it working. Sometimes settings AND a new SIM are needed.
BTW, I'm confused by this .
I go abroad from the USA for long stretches,
are you visiting the USA or leaving the USA?