Very probably not all services will accept a foreign (Thai) phone number.
Your iPhone can handle one SIM and 8 (or more?) eSIMs.
You can either keep a separate cheap phone for the SMS from the banks and others, or get your uk (or the Thai) number as eSIM.
If you go for a cheap phone:
- it can be a PIA to keep it charged
- it can be a PIA to have to start it before receiving a code
- if it’s too old it cannot do WiFi calling
Been there ;)
WiFi calling isn’t well known.
When turned on, and you’re in WiFi, your phone behaves as if it was in the providers country. I use that to call Swiss companies and government without roaming charges.
A visa is used to enter the country. Once you enter, a visa is used(!) and you get a stamp saying how long you’re allowed to stay(!).
That’s also the reason why it’s call extension of stay and not extension of visa.
So if you don’t get a visa before entering, you don’t have one and you will not get one. You get a permit for staying in the country. That’s what the stamp is for.
I’m not a native English speaker, but I wonder that you don’t understand what an exemption is.