You must have seen different tips and tricks on how to turn-off iMessage. Believe me I have tried them all and none seem to work. Those who still had iPhones/iDevices who tried to contact me via iMessage had their messages either go through or bounce back. The system rarely diverted them to me via SMS. Therefore, I lost a lot of incoming and probably some friends along the way:)
Needless to say after many complaints Apple actually released a tool that works.
1. Go here: https://selfsolve.apple.com/deregister-imessage
2. Type in your phone number
3. Receive a 6 digit text message and type that into the browser
Enjoy cutting the final strings from Apple 😉
PRO TIP: The link only works via browser. If you try with your handheld, it will load, but it will not send you a text message after you type in your phone number. Go figure. Use a fully functional laptop.