How to Remove Your Phone Number from iMessage
For a long time, there was no way for users switching from an iPhone to an Android/Windows phone to deregister their phone numbers from iMessage, leading to lost messages. Apple finally introduced a tool for de-registering phone numbers in November, and this video tells you how to use it.
Deregister tool: https://selfsolve.apple.com/deregiste...
http://www.macrumors.com/2014/11/09/a...