SIM swap is no problem but if you buy the phone in US you will have problems unlocking it legally in the UK. Make sure you buy an international version as well in case you get one with different bands that don't work in the UK.
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)