This September, we will be doing the RS tour Best of the Adriatic and were wondering about a sim card for an iPhone 6S using it in Slovenia and Croatia, plus southern Italy. The real issue, will one card work for all three countries and where is the best place to buy it? Are they priced based upon amount data usage?
From June 15, roaming costs within the EU will largely be abolished, so it does not matter which country you buy it in. It would have worked abroad in any case, but now there will be no surcharges involved, too. The only issue to consider is whether the provider offers online top-ups, as it is the only way to add credit outside of the SIM card's home country.