Just a heads up about people’s suggestions on signal. If you don’t open your desktop client often and it needs to be logged back in it will not sync your latest notes to self messages (perhaps other messages too).
A phone plan with a phone. You pay more over time and you get stuck with a contract.
Buy a phone and get a plan from a MVNO. Your monthly plan will be better and cheaper. Also since you own the phone when a better plan appears you can just switch.
I spend lots of time in south korea and VPNs are fine to use. I primarily use mine for getting around region blocks or for added privacy when on public networks.