Apple has posted a new tool that lets you deregister your phone number from iMessage.
You may need to turn off iMessage if you are now using a non-Apple phone and can’t get SMS or text messages someone sends you from an iPhone.
The tool resolves an issue with Apple’s messaging system that manifests when switching from iOS to another operating system while keeping the same number. Often Apple’s system doesn’t recognize that your number is no longer associated with an iOS device. Consequently, messages from other iOS users are still sent via iMessage, which can’t be received on the new device, resulting in a large number of unreceived SMS messages.
Thankfully, you can now input your number into this form to deregister it from iMessage.
If you’ve been experiencing this problem, give the tool a try and let us know in the comments if it resolves your issues!