… if you have roaming coverage.

And even in that case, doing this for a long period of time violates most roaming policies

Even with fair usage policy violations (like long term roaming) the prices are still quite reasonable: 1.30 EUR/GiB (+VAT); from next year 1.10 EUR/GiB (+VAT).

https://en.wikipedia.org/wiki/European_Union_roaming_regulat...

The only thing that happens is your data becomes a lot more expensive, the card still continues to work as normal. I've not lived in Poland for over 15 years now, and I still have a polish SIM card that I use almost daily - the only thing that I've lost due to roaming long term is cheap data packs, I can still call and text as normal from my monthly allowance.

Maybe in the countries that you are familiar with that is the case.

In some places your plan will be cancelled for roaming beyond a certain number of days or quantity of usage. Telecom laws and polices vary widely.

There's eu(maybe even EEA?) wide free roaming legally mandated since I think 2017 or so? But it's not a permanent solution, your second paragraph still holds true.

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I know of some UK SIMs that do not roam.

That's because we are no longer in the EU. Before Brexit they were legally mandated to allow free roaming in the EU. Now they are back to charging whatever outrageous prices they wish.

As far as I know it is only EU. Both UK and Switzerland have some operators that roam and some that do not. fwiw, fastweb in Italy provides roaming in both and has a very generous fair usage policy.