Talk:Greece/@comment-108.33.114.79-20160229010009/@comment-24682153-20160229215753

Yes. SIM cards will work in both countries. Vodafone has even a network in both. But unfortunately, you will pay steep roaming surcharges in the other country. Turkey is (unlike Greece) not in the EU. So roaming is not regulated. This also applies to Turkish SIM cards in Greece.

Vodafone in Greece sells a 'Daily Travel Pack' at €3 with 30 mins, 30 SMS and 100 MB per day roaming in Turkey see here. But this may change in May as new EU regulations will implemented (and the package is mostly for the EU). So check their site later again.

As you can read below in the comments, you will not be able to buy a SIM card at ATH airport. You'll need to wait until you get to town.