Originally Posted by
ajeleonard
Any SIM card / plan from any EU country works the same in any other EU country with no extra charges, it's required by law. Buy one in the first country you visit and it will work for the rest of your trip
While this is true, it still depends on the actual plan (be it subscription or pre-paid) which you have. There are definitely examples of the cheapest pre-paid packages which do not have international roaming in the EU, as well as other plans which might have data caps if you head abroad.
For example my own subscription gives basically unlimited data in Romania, while having only 5GB or so roaming a month in EU countries (of course, you can buy more if you need/spent the data). I know of several other countries where similar data caps are in existence with most of the packages with local providers.
While I cannot advice what to buy as I have never bought a SIM card outside the countries I resided in within Europe, I would advice you that if you buy a SIM card in a local store in Europe to make sure you ask specifically if there are any such caps, and if there are, how easy it is to pay for extra data while on the road (most providers have the option to pay through the provider's online shop if you happen to be in another European country than the one where you bought the SIM card, but ask this in advance).