How to stop all iPhones in the house from ringing at the same time on incoming call
1. Go to your iPhone's Settings menu, and hit the FaceTime feature;
2. In the FaceTime list you will see an option titled "iPhone Cellular Calls," which is turned on by default;
3. Switch the slider to the "off" position, and do it on all other iDevices that are associated with your iTunes, iCloud and so on Apple ID accounts;
4. That's it, now incoming calls won't be ringing across your household, regardless of who they are meant for.
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Things that are NOT allowed: