Apple releases Deregister iMessage online tool. If you recently switched from using an iPhone and didn't turn off iMessage, your number is still sending iMessages, not SMS or text. You might need to deregister iMessage if you have a non-Apple phone and can't get SMS or text messages someone sends you from an iPhone.
This can happen if you used iMessage on your iPhone and then transferred your SIM card or phone number to a non-Apple phone (such as Android, Windows, or BlackBerry).
|Apple releases Deregister iMessage online tool|
How do I deregister iMessage?
1. If you still have the iPhone you were using before you switched, use it to deregister iMessage with these steps.
2. If you transferred your SIM card from the iPhone to a non-Apple phone, put it back in the iPhone.
3. Make sure that you're connected to the cellular data network.
Tap Settings > Messages. Turn iMessage off.