The terminology associated with sending text messages from your iPhone can be a little confusing. One of these terms is “SMS”, which stands for “short messaging service.” It’s essentially synonymous with text messaging, but it somewhat different than your iPhone’s iMessage option. Fortunately the iPhone tries to help you distinguish the different types of text messages by adjusting the color of the bubble around the text when you send it.
A blue text message means that the message was sent as an iMessage, which means that the recipient is an iPhone user that has enabled iMessage on their device. A green text message means that the recipient is not using iMessage. Typically this indicates that the recipient has an Android device.
But since the iPhone can determine this on its own, you may be wondering what the “Send as SMS” option means in the Messages menu on your iPhone. This option allows you to choose whether or not your iPhone should send an iMessage as a regular SMS text message in the event that it’s unable to send as an iMessage.
How to Enable or Disable the “Send as SMS” Option on an iPhone
The steps in this article were performed on an iPhone 7 Plus in iOS 12.2.
Step 1: Open the Settings menu.

Step 2: Scroll down and choose the Messages option.

Step 3: Tap the button to the right of Send as SMS to turn it on or off. In the image below my iPhone will attempt to send my iMessage as an SMS in the event that the iMessage version fails to send.

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Gary Thompson has been in IT consulting since the mid 2000s, and enjoys writing about mobile devices and computers. His primary topics of interest include iPhones and Windows, but he has written about many other devices and applications.