[ThePowerOfFuet]

This is not correct; you are conflating FaceTime and iMessage.

If you insert your SIM in an iPhone or iPad, then yes your number will be registered for iMessage and all iOS users will default to iMessaging you.

You cannot FaceTime to or from your phone number without your SIM being inserted in the device. In the absence of this, you can FaceTime just fine using your Apple ID as the identifier.

[forgotmypw17]

I promise you, this exact thing happened to me.

I had never used my number with an Apple device, I only registered my email and FaceTimed someone.

Maybe I gave Apple my phone number at some point.

One day, I looked at my Apple device after not using it for a while, and discovered a handful of text messages which had been forwarded there -- you're right, to iMessage, not FaceTime -- on the Apple device.

I never received them on my actual number.

[ThePowerOfFuet]

Everything I know (and my expertise on this topic is pretty good) indicates that a phone number cannot be registered for iMessage without a SIM carrying that number being inserted into an iPhone or iPad.

Other devices signed into the same iCloud account can then use that number as well.