FaceTime: Unable to receive calls or add phone number

Re: "FaceTime: Unable to receive calls or add phone number"

Wondering which iOS version is installed on your iPhone 16:

More info: About iOS 26 Updates - Apple Support

To ensure you have the latest bug-fixes and security updates, you can check for iOS updates in Settings > General > Software updates.

Reminder: If you choose to update iOS, it wise to back-up your iPhone first,

Else: You may want to try trouble-shooting by checking for interference:

See:  If your device has network connectivity issues, check for VPN and other third-party security software - Apple Support 

or

How to: Resolve Wi-Fi and Bluetooth issues caused by wireless interference - Apple Support

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Re: "I had my number and Gmail selected already and then after a while it wouldn’t let me put the number back on but it wasn’t grey and it would still load after I push it "

You may want to check your phone number is listed correctly in Messages or FaceTime Add or remove your phone number in Messages or FaceTime - Apple Support

Eg: says:

"Set up your phone number

On your iPhone:

1. Go to Settings. Tap Apps, then select Messages. Make sure that iMessage is on. You may need to wait a moment for it to be activated.
2. Tap Send and Receive. (If you see “Use your Apple Account for iMessage”, tap it and sign in with the same Apple Account that you use on your Mac or iPad.)
3. In the “You can receive iMessages to and Reply From” section, make sure your phone number and Apple Account are selected.
4. Go to Settings. Tap Apps, then select FaceTime. Make sure that your phone number and Apple Account are selected in the "You can be reached by FaceTime at" section."