Can we identify the caller

Rohit_Iphone wrote:

or can we know that how many people from my contact list are using iPhone?

The latter is not possible.

However, before sending an individual message you will know it.

Use message app > select a contact on To: < > then you will see greyed out "iMessage" or "Text Message" in the Text box below

iMessage indicates the contact is using an iPhone and have enabled iMessage

Text indicates either the contact has not activated iMessage or has a non-iOS device.

See the pic below for better clarity

Not from a call but if they send you a text or you send them one

Android - green

Iphone - blue

and if you look at each contact the Apple users should have Facetime as an option but they could be only ipad or Mac users