Pro tip if your leaving ios for droid use a new phone number, apple will never remove that number from its icloud servers which causes some issues with alerts and messages in the future
You can easily remove your number from iMessage and FaceTime, even after the fact.
Deregister and Turn Off iMessage - Apple Support
Learn how to deregister iMessage. Be sure you can keep getting text messages by providing the phone number you want to deregister from iMessage.