You may find yourself in a similar situation. We had to remotely erase the wife’s iPhone this week and then tried to get it back up and running normally. iMessage was not working properly, the iPhone could log into iMessage using email, but it would not log in using the phone number.

iMessaging via the phone number was our goal. Messaging from an email address to a phone number wasn’t what we were looking for.

So I did what every red blooded American would do, I jumped on the interwebs and found all sorts of “turn it on and off”, “reset network settings”, “log out of iCloud/App Store” etc. Nothing worked.

Finally I went to Apple who told me to restore the iPhone after telling me to do the same steps above. Then they suggested something easier than everything I’d already tried:

1. Log out of all the other devices that use iMessage; in our case that was an iPad and a Mac.
2. Activate iMessage, making sure you’re already logged out is iMessage, i.e. make sure you don’t see an Apple ID with your email already in there
3. You might have to toggle that back and forth a bit or even go on and off of a Wi-Fi connection. That’s what seemed to work for me.

I believe what was happening was that the phone number associated with the iMessage account needs to activate first. For me it worked when I switch back to Wi-Fi after trying to do it over the carrier network. Once I was on iMessage with the phone number I could log in using the Apple ID. Then we logged back into the other devices which then reallowed us to send/receive via the phone number.