How do I know if my phone is CDMA or GSM?
How can I determine whether my iPhone 7 is CDMA or GSM?
Dell Laptop-OTHER, Windows 7
Check the model number on the back of the phone ( more details, see: Identify your iPhone model - Apple Support ).
The A1660 is both GSM and CDMA.
The A1778 is GSM only.
More details, see the "Cellular and Wireless" section of iPhone 7 - Technical Specifications - Apple