Re: Facetime on mac only : Can I use FaceTime on a MacBook Air without an iPhone?
Yes. Facetime calls on a Mac use wi-fi between Apple users, so this doesn't require use of a cell-phone
Getting started with FaceTime on Mac
See: FaceTime requirements on Mac - Apple Support
and how to:
Sign in to or out of FaceTime on Mac - Apple Support
More on how to: Use FaceTime on Mac - Apple Support
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As your screenshot shows: if you were to have an iPhone connected :
FaceTime could also be used for phone calls (cellular audio to a phone number)
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Useful Resource: FaceTime User Guide for Mac - Apple Support (Use "Table of Contents" at the top for details)