The Problem:
You switched from using an iPhone to another type of phone. Your friends send you SMS messages from their iPhones but you do not receive them on your new phone.
The Cause:
Apple's iMessage feature is linked to your phone number. When your friends send you an SMS, it comes through as an iMessage Since you no longer have an iPhone, you do not receive those iMessages
The Solution:
You need to deactivate iMessage on all your apple products. Follow the steps below to fix this problem.
Disable iMessage On All Devices You Have Access To
On EVERY one of your ios Apple devices (iPhones, iPads, iPod touch):
  1. Go to Settings
  2. Go to Messages
  3. Move slider to Off for iMessage
On EVERY Apple computer you own:
  1. In Finder or Searchlight search for "messages.app" to find the messages app
  2. Click on the message app ( it has a blue and white bubble icon )
  3. If you are signed out, sign in using your apple id
  4. Go to messages preferences
  5. Uncheck "you can be reached for messages at" next to your phone number
  6. Click "sign out" button at top right
  7. Quit iMessage
If You No Longer Have Access To A Device (lost, stolen, broken)
  1. go to Apple Support Profile
  2. Log in with your Apple Id and password
  3. Click on each product that you no longer have access to and click un-register
If The Above Does Not Solve The Problem
  1. Call support: 1 800 694 7466
  2. Tell them that you switched from iphone and want to disable imessaging to your phone number
  3. They will ask for your phone number and disable the certificate
Note
  • Some people still have trouble after following those steps. Keep calling Apple customer support if you are one of those.
  • If your friend gets a "Denied" message when sending you an SMS, it means that they do not have the "Send SMS when imessage fails" option checked in their settings under messages. You would have to ask them to turn that on.
  • Apple Support Discussion on this topic.