Q: I recently changed my iPhone number with my cell phone company after moving back home from University by going to my account on their web site. The change seems to have taken affect for my phone calls already, but I’m wondering if there’s anything special I need to do to change it for iMessage, as I’m still receiving iMessages to my old phone number and text messages to the new one. Also, what happens to iMessage on my other devices like my iPad and my Mac? Do I need to do something to change the phone number there as well?
A: Unlike SMS messages, which travel over your carrier’s network and are directly tied to your phone number, iMessages travel over the Internet via Apple’s servers. Your cellular phone number is used as an iMessage “address” to make this process as transparent as possible, but is not directly tied to your carrier’s network.
What happens is that when your iPhone is setup for iMessage, your cellular phone number is registered with Apple by sending a hidden SMS message to Apple’s servers. Since this SMS message comes from the phone number assigned to you by your carrier, this allows Apple to verify that it’s a correct and valid phone number, and allows iMessage to “just work” without requiring the user to go through a potentially complicated manual validation process.
To allow your phone number to be used for iMessage on other devices such as an iPad, iPod touch, or Mac, your iPhone automatically associates it with your Apple ID once it’s been verified and assigned to your iPhone. So basically, any phone number associated with iMessage on your iPhone will automatically be available to your other iOS and OS X devices, provided they’re signed in with the same Apple ID. Again, this process is designed to be entirely transparent.
When you change your phone number with your carrier, the carrier network sends out an internal message to your iPhone to notify it of the new numberer, and your iPhone should re-register with iMessage using the new number as soon as it detects this update, although sometimes it may take a few minutes for this to take effect. You can confirm which phone number is being used for iMessage by going into Messages in your iPhone Settings app and selecting the “Send & Receive” option. This will show you the phone number(s) and addresses that you can receive iMessages at.
If your new phone number is not appearing here, you can go back to the prior screen and simply toggle iMessage OFF and back ON again, which should for it to re-register with Apple’s servers using your new phone number. When turning iMessage back ON, you should see a “Waiting for activation” status and the “Send & Receive” list will only show your Apple ID e-mail address(es) as being active. Once iMessage activation completes, your new phone number will appear selected, and should also be pushed to your iPad and the Messages app on your Mac. Your old phone number should also disappear and be removed from your Apple ID once the new number is registered.
If iMessage activation fails to complete properly, or your old phone number still appears in the iMessage addresses, you can try powering off your iPhone and powering it back on again to see if this forces it to pick up the new phone number.
If you’re still having problems activating iMessage even after this, you will want to confirm with your cellular carrier that there aren’t any restrictions on sending SMS messages as part of your plan; since iMessage (and FaceTime) registration requires an SMS message to be sent to Apple’s servers, blocked SMS messages can cause the activation process to fail.