Hi @Fotis1975
Thanks for coming to the community.
If you're account is pay as you go, please see our Pay As You Go Charges for Roaming in the EU, Help page for information on using your pay as you go SIM in Greece.
If you have a pay monthly account, our Changes to EU Roaming, Help page has full details on roaming charges and add-ons.
Let me know if you have any questions.
Leanne.
