iMessage vs SMS/MMS

                   Have you ever noticed some of your message bubbles are blue and some are green?

​Set up or remove a phone numberUse these steps to set up or remove the number for your iPhone for Messages and FaceTime on other devices. If you use this feature and share your Apple ID with someone, you can't prevent them from seeing your conversations (Instead of using the same Apple ID as someone else, set up Family Sharing).
Set upYou can set up only the phone number that belongs to your iPhone:

1. On your iPhone, tap Settings > Messages. Check that iMessage is on. You might need to wait for it to activate.
2. Tap Send & Receive. If you see “Use your Apple ID for iMessage,” tap it and sign in with your Apple ID. This should be the same Apple ID that you use on your iPad, iPod touch, or Mac.
3. Under “You can be reached by iMessage at,” make sure that there are checkmarks beside your phone number and Apple ID.
4. Go to Settings > FaceTime and use the same steps.
5. Now you just need to turn on your phone number for your iPad, iPod touch, or Mac. Use the following sections to learn how.

RemoveIf you don't want calls or messages for your iPhone on your iPad, iPod touch, or Mac, you can remove your phone number. There are two ways to do this:

• On your iPhone, go to Settings > Messages > Send & Receive. Sign out of your Apple ID account. Then go to Settings > FaceTime and sign out of your Apple ID account.
• If the phone number that you want to remove belongs to an iPhone that you can't access, change your Apple ID password. This removes all phone numbers from your iPad, iPod touch, and Mac. Calls or messages for the removed numbers won't appear on those devices anymore.