ヨーロッパ周遊SIMカードの現地購入について

意外と周遊SIMを購入するのは苦労します

周遊するならEU各地で使えるSIMが欲しいですよね。
2017年にEU各国での利用に際してローミング費用かからなくなりましたが、そもそもEU内でローミング可能なSIMの購入が困難な国もとりわけ東欧では多いです。
また、西欧でもドイツは旅行者がプリペイドSIMを購入するのは難しいですね。SIMを購入するのにおすすめはオーストリア。価格も安く簡単にローミング可能なSIMを購入できます。

Roaming in the EU

europa.eu
全てのSIMが対応している訳ではく、特にMVNO系は非対応の場合が多く、さらにいくつか条件があります。基本的には、EU内で大手通信業者のを買えば、他国でも使えます。

Conditions
Fair use policy
Fair use policy and data limits
When you roam like at home there are no volume restrictions for voice calls and SMS, but there are rules and limits for data usage at domestic price which are determined by the type of contract you have.
n some specific cases (see below), beyond a reasonably high volume of roaming data at domestic price, you may have to pay a data roaming surcharge which will be equal to the wholesale (EU-wide) data cap (€4.50 / GB of data in 2019 plus VAT). This wholesale roaming price is the maximum your domestic operator has to pay a foreign operator when you use data roaming services.

Data limits - pre-paid cards
If you have a pre-paid card (meaning that you pay in advance for using your mobile phone) you can roam like at home. However, your mobile operator may apply a roam like at home limit for data if you pay per unit and your domestic unit price for data is less than €4.50 per GB.
などなど・・・。

>その知り合いの方はイタリアのvodafoneのSIMカードを買ったそうです

これは、2017年6月以前の昔話し（に近い話）でしょう。今は、意味ありません。

ではバルト三国で。
prepaid-data-sim-card.fandom.com
Estonia
Telia (formerly EMT, owned by the Swedish Telia Group)
Elisa (owned by Finnish Elisa Oyj)
Tele2 (owned by Swedish Tele2 Group)

Top-ups
While being within the country, you can buy voucher codes at many outlets. But it's a different story from out of the country.

It's still a problem to recharge Estonian mobile numbers from abroad without having an Estonian bank account even if SEPA top-ups from European bank accounts should theoretically work (see Telia below). There are no credit card payment options for Estonian SIM cards. Furthermore, there are no 3rd party dealers or agencies who recharge Estonian SIM cards online. So if you want to top-up an Estonian mobile number from other countries, take vouchers with you or find an Estonian friend, who will buy it for you while staying in the country.

EU roaming: no Roam like at home?
In light of very low domestic prices for data, EU roaming is charged very high. The providers all charge 0.9c/MB equal to €9.24 per GB, which is pretty expensive for roaming. That's why you should buy a SIM card only for domestic use in Estonia and look for a SIM for EU roaming better somewhere else.

だそうです。この国の特殊制。下まで読めばわかりますが、この国でEUローミング用のSIMは買わないほうが良い。でも、この国が恐らく一番進んでいる筈なので・・・。

Lithuania
Telia - prepaid brands: Ežys and Extra
Tele2 - prepaid brand: Pildyk
Bitė - prepaid brand: Labas
ここはもっと遅れている（LTEなど）ようだし、EU roamingの記載がないので、ここも没。

Latvia
LMT
Tele2
Bite
In 2019 Tele2 and Bite signed a network sharing agreement for Latvia and Lithuania.

EU roamingはやっているのですが、、、高い・・・のでここも没でしょう。

この三国はドメスティックSIMで切り抜けて、西欧に出た時に買いましょう。
prepaid-data-sim-card.fandom.comで該当する国に行けば、少なくとも日本人の書いた日記みたいなものよりかは正確な情報が得られます。