Add new property to Phone entity to mark a number as a mobile phone or the primary SMS number.
Currently we don't have a straightforward way to say "this is a mobile phone/cell phone number" we have the
phone_type property but being an option group it's inherently unreliable and subject to change. If we were looking for a way to say "this phone number is a mobile phone - use it for sending SMS" we're kinda out of luck!
We can try to infer whether a phone number is for a cell phone by checking for phone_type but it's unreliable and we can't reliably rely on a single ID designating a mobile phone number (or that any of them do!)
An explicit property that denotes that a number is a cellphone/mobile number or alternatively a property that denotes that that number is the preferred for SMS e.g