How to trun off iMessages on iPhone before switch to a new Samsung phone?

Problem about switching iMessags from old iPhone to Samsung Galaxy:
“I had the same problem switching imessages from iphone 5 to galaxy s6. When I originally made the switch I put my old phone number on my new galaxy and switched the iphone to a new phone # so I didn't have the problem. The problem occurred when I switched back to my iphone and then switched again to the galaxy. Confusing, I know! Anyhoo, I think the problem is when the phone number is attached to the sim card! After I reswitched back to my galaxy, my phone # was still embedded on my iphone 5 and I could not uncheck it. I have several lines so I changed my iphone to an unused # and it solved the problem. And I dont want to be charged the data fee so I just switched the line back to a basic phone. But switching my iphone to a different number, even for a min, seems to solve the problem. That leaves me to believe it is because the phone number i am using is attached to the sim card. I only thought of this today and did not try removing the sim card? That may work too. Hope this helps some of you. I know its a little confusing. Bottom line, I like switching between the 2 phones on my main phone number, but I need to unattach my main phone number from my sim card to free it up from sending imessages to my phone number on my iphone.”--Ask by kerryfromperrysburg in discussions.apple.com

How to deactivate iMessage and before switching from iPhone to Android Samsung Phone? Want to Using iMessages after switching from Appple iPhone to Android Samsung?

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.

Tips：To avoid disruptions in text messaging service when transferring from iOS, please read this use guide about:
how to transfer messages between iPhone and Samsung directly with third-part phone transfer tool.

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 2 options below:

If peers enable the option to send as a text message, they can then communicate with the Android user.

Way 1: Disable iMessages on your iPhone

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.

Follow the instructions below to disable iMessage on your iPhone® before switching to Samsung Android™

Step 1: If you have already switched from iPhone to Samsung, remove your SIM card from your Samsung smartphone and insert it in your iPhone.
Step 2:From the home screen of your iPhone, select Settings  >  Messages .
Step 3:Set the iMessage switch to Off.

Step 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.

Way 2: Deregister your iPhone

Follow the instructions below to deregister the iPhone® that you switched from:

Step 1: Go to https://selfsolve.apple.com/deregister-imessage.

Step 2: Enter your phone number, and click Send Code.
Step 3: When you receive the confirmation code, enter it and click Submit.

Read more:

How to Recover lost SMS from Samsung phone

How to Recover lost SMS from iPhone on iOS 9