Yeah, all that OP has to do is go into the settings on the iPhone and either unlink the phone number or disable iMessage entirely and it'll go back to normal. I

Yeah, all that OP has to do is go into the settings on the iPhone and either unlink the phone number or disable iMessage entirely and it'll go back to normal. It just required some forethought other than simply wiping the phone. I don't understand what the issue is; the feature is there so that you can be iMessaged if your phone happens to be turned off for a few days. If the phone number was de-linked immediately what would the use in that be? It expires after 10 days, anyway.