Just wanted to update for anyone looking to purchase SIM cards when arriving in Athens. There are 2 locations in ATH where you can buy them, to give you Data and voice service while in Greece. We used the Vodaphone kiosk, on lower level of airport, close to “Exit 2”. The clerk who served us was very helpful: she installed the new SIM card, verified its operation, explained the different codes and phone numbers. €32 for 10 Gb, with 200 minutes talk. (Puts our brutal Canadian plans to shame!!).
You will need to show your passport. Allow 20-30 minutes; they take their time to make sure each client is activated before leaving, so it is a bit time-consuming, but worthwhile, especially if you are leaving for an Island, and/or not sure where you’ll find a provider.
There is a second spot to buy, according to Airport Info booth, on the 2nd floor around security check, but we did not check it out.
Hope this helps some folks!!