Deregister iMessage on your iPhone
If you still have your iPhone, you can deregister iMessage with these steps:
- If you transferred your SIM card from your iPhone to a non-Apple phone, put it back in your iPhone.
- Make sure that you're connected to your cellular data network.
- Tap Settings > Messages and turn off iMessage.
Deregister iMessage online
If you don't have access to your iPhone, you can deregister iMessage online. After you complete deregistration, your phone number is removed from iMessage services. You should be able to receive text messages right away but it might take a few hours for some Apple devices to recognize that you're not using iMessage when they send you a message.
If someone sends an iMessage to your Apple ID, you'll get it on your other Apple devices. If someone sends a text to your phone number, you'll get the message as an SMS/MMS only on your phone.