Buy a 2nd-hand $40 scrap phone, erase it, save a few panorama pictures and a couple of selfies on it and put your SIM card in it every time you are about to cross a border. Then put the card back in your regular phone after that.
It is less "sim card is tied to this phone and can't be moved" and more "sim card exists logically and doesn't require a physical presence in the phone it wants to be used in"
Which really sucks for travellers. High roaming costs? Just go to a gasstation and buy a travel sim card, put it inside, use it, put it in the walled when you leave, and if you still have any data left, use it the next time you come there.
Just go to a carrier website, buy an esim, download to the phone, use it, switch it off when you leave, use it next time you come there.
It is literally the same except you don't even need to go to a gas station. My Pixel can hold as many esims as I want standing by until they are needed to be used.
If any company you depend on uses your phone number for 2FA, then SIMless is useful. A SIM can be removed and put into another phone to receive authentication txts.
Mostly relevant if your phone is lost or stolen, or perhaps even if criminals are directly threatening you. For example, I worry about bank accounts when I travel to some countries because criminals would be highly motivated to steal from me - the only thing protecting me is their ignorance. In some countries a few thousand dollars is a lot of motivation. Unfortunately my primary bank does not provide secure 2FA but only provides phone auth, and I am locked into my bank because of my mortgage (I have a mortgage, and conditions have changed which prevent me from getting a different mortgage from another bank). I could cancel revolving credit (the main financial risk) but that has other opportunity costs for me.
Also SIMless helps prevent unwanted telephone charges - important if roaming in other countries on account. Phone companies do not make it easy to limit your liability, so if you are unlucky you could end up owing many thousands.
This is why you should enable the PIN code feature for your SIM. It will be disabled after a few incorrect attempts. It protects you from the scenarios you describe.
