If you have previously set up an old iPhone, you may have missed a few messages from others who also use iMessages. There are a couple reasons might want to deregister from this service:

• You no longer use an Apple device
• Remove any notifications asking you to set up iMessages or FaceTime
• No more "blue texts" in the Messages

By following the steps below, you are disabling access to iMessages on your new mobile phone and your previous iMessages will no longer be recovered. Your messages will also 
Note: You will still be able to contact people with iMessages, as it is tied to that person's mobile number.

1. Insert your SIM card into your Apple device.
2. Go to  Settings, select  Messages.
3. Turn iMessage off.
4. Go back to Settings and select  FaceTime.
5. Turn FaceTime off. Exit Settings.

If you no longer have an iPhone or other Apple device, but have access to the mobile number, please use Apple's Self-solve website.

1. Visit the Apple self solve website: https://selfsolve.apple.com/deregister-imessage/
2. Enter the phone number you want to deregister from iMessage and Apple will send a confirmation code.
3. Enter confirmation code. Enter the 6-digit code sent to the mobile number and submit to complete deregistration.