@pml. I have an Apple Watch and an Apple iPhone. The Apple Watch can be synced with your iPhone with bluetooth and you have to have your iPhone in range of Apple Watch to use it as your device for calling and receiving calls.
You can also get an Apple Watch that is set up for cell phone service. That's what I did. There are additional charges with your cell phone company if you decide that you want an Apple Watch to use for messaging (texts), email, and phone calls when you don't have your iPhone with you.

Compare Apple Watch Models:

-- https://www.apple.com/watch/compare/