How do I turn off iMessage on my old iPhone before I switch to my new Android device?

Cell Phones: How do I turn off iMessage on my old iPhone before I switch to my new Samsung device?

How Do I use iMessage after switching from Apple® iOS to Samsung Android™

After using Samsung Smart Switch to switch from Apple® iOS to Samsung Android™, previous conversations that took place over iMessage® can no longer be replied to and new messages from peers are not received by the Samsung Android™ smartphone.
The mobile number being used by the Samsung Android™ smartphone is associated with the Apple Support Profile that was originally registered to that user's iPhone®. To resolve this, please follow the steps in one of the the 3 options below:
iMessage not delivered
If peers enable the option to send as a text message, they can then communicate with the Android user.

Option 1- Disable iMessage on your iPhone®

Follow the instructions below to disable iMessage on your iPhone® before switching to Samsung Android™
  1. If you have already switched from iPhone to Samsung, remove your SIM card from your Samsung smartphone and insert it in your iPhone.
  2. From the home screen of your iPhone, select Settings Settings > Messages Messages.
  3. Set the iMessage switch to Off.
    4. Disable iMessage
  4. If you removed your SIM card from your Samsung smartphone and inserted it into your iPhone in step 1, remove it from your iPhone and insert it in your Samsung smartphone.
Note: If you have other iOS devices (iMac®, iPod® Touch, iPad®, etc) iMessages sent by peers will continue to be received on those devices, but not on your Samsung Android™ smartphone.

Option 2 - Deregister your iPhone®

Follow the instructions below to deregister the iPhone® that you switched from:
  1. Go to https://selfsolve.apple.com/deregister-imessage.
    2. Deregister your iPhone
  2. Enter your phone number, and click Send Code.
  3. When you receive the confirmation code, enter it and click Submit.

Option 3 - Change the password for your Apple ID

  1. Go to https://appleid.apple.com.
  2. Click on "Manage your ID" OR "Reset your password".
    3. Reset Apple ID
  3. Click on "Password and Security".
  4. Answer the Security Questions that were set when you created the Apple® ID.
  5. Under “Choose a new password”, click “Change Password”.
This will trigger iMessage to send messages using SMS.
Note: If you are using iMessage on multiple iOS devices (iMac, iPod Touch, iPad, etc), when the new password for the Apple ID is entered on the other iOS device(s) delivery of messages to the Samsung Android™ smartphone will be interrupted unless the password for the Apple ID is changed again.
Note: Changing the password will disconnect iPhone from the iCloud/iMessage system. If your iPhone is taken out of the picture, when another iPhone user sends a message to an Android user, the Android user will get an SMS, as long as he/she had his mobile phone number under contacts.

Source: http://www.samsung.com/us/support/faq/FAQ00053450/62989/SM-N910AZWEATT