Please visit the official website of the phone manufacturer (Apple, Samsung, Nokia etc), to confirm sim card compatibility for the phone you're planning to buy.
Also, just a heads up: phones are delivered without a sim card. If you'd like to purchase one, please contact a telecom company directly.
To make sure that your sim card/mobile plan is compatible with a phone sold on Back Market, we suggest that you ask your mobile network provider directly whether your current service and sim card are compatible with the phone model you are buying.