More cost effective - a Greece SIM card or Consumer Cellular International Roaming?

Can your phone take an e-sim?

There are plans for 14 days that cost less than $30.00. I have used a European eSIM or physical SIM on 8 trips without any problem in my iPhone. Usually use around 5-6 GB of data on it per trip along with WiFi in the hotels. Vendors in the Athens airport charge an extra €12.50 for a plan. If your iPhone utilizes an eSIM order one ahead of time to save standing in line at the airport. There is a web site (Traveltomtom) that has recommendations for Greece.
Also if you do not have a VPN app for your phone recommend using one when you connect to any WiFi.

Ditto the E-Sim. We use Holafly.

I always get a Cosmote SIM card when I arrive in Greece.

Available at Germanos Stores or even from street sellers in Athens.

There is a Vodophone kiosk at the airport but doesn't sell Cosmote SIM cards but I hear it works well also.

Inexpensive and works well all over Greece including rural areas.

I used consumer cellular international coverage for my recent 26 days in Italy. I use my phone continually for google maps, reading history of places I’m touring during the day, texting my husband and others etc. I never did make any phone calls. My bill came to roughly $17. I’m definitely doing it again in Oct when I go to France.

After Lyndash's reply I opted for CC AND the reason my phone would not be covered under warranty is that until I own it, it is locked and wouldn't accept a SIM card. That would have been interesting since CC activates the phone before it leaves the US. Would have been a great way to start a vacation with my wife's flip phone.

Of course your CC rep said not to use foreign SIM cards. They want you to use their service. I haven’t changed the sim in my Xr since I bought it as new 8 years ago. Have always used an eSIM. Much easier and one’s phone doesn’t need to be unlocked. Beware though, while European companies aren’t allowed to charge roaming fees, American companies suffer no such regulations and the fees can be extraordinarily high. While I understand that your phone is still locked to CC you could always call and ask them to unlock it for just your trip. I did that in 2023 when I discovered that my wife’s phone was still locked to T-Mobile, which we still use, and they unlocked it for our trip. When we returned we just paid the rest off and it was unlocked thereafter.