If you still have your iPhone
Getting rid of iMessage is easiest to do if you still have your iPhone and are just about to trade it in for something different.
Step 1: Go into Settings and then scroll down to Messages
Step 2: Once in Messages, toggle switch at the top next to iMessage.
All of the messages sent to this number will now be SMS.
If you’ve already made the switch
Most people realize this is a problem only after they’ve already started using their new phone. For these people, Apple set up a site where you can deregister your iMessage.
Step 1: Go to the site and scroll down to the second option. Plug in your phone number.
Step 2: You will be sent a confirmation code in a text message. Enter that code into the space provided at the Apple webpage and you are set.
Apple said that it might take a few hours to work so wait awhile before you begin drawing up a lawsuit of your own. After using this process, you are still able to receive iMessages on an iPad using your email address and Apple ID, but they will be turned to SMS if sent to your phone number.
These two methods should do the trick if for some reason you’re still not receiving messages from certain people, there are a couple things to try. You can ask them to delete and reenter your number into their phone and start a new conversation with you. If you still can’t get it to work, contact Apple Support.