How to turn on SMS function on my iPhone? I want to send messages to my friends who are not using iPhones.

If your friend is not using an iPhone, you can not send or receive iMessage text with him. You have to turn on the MMS function on your iPhone to exchange large messages with him.

1. Go to "Settings > Messages". You see a list of settings for the Messages app.

2. Scroll down and turn on the "Send as SMS" switch. The "Messages" app will behave as below:

• Use the iMessage technology over Wi-Fi Internet connection, if available.
• Use the iMessage technology over cellular Internet connection, if Wi-Fi is not available.
• Use the MMS technology, if Internet connection is not available and the message is large.
• Use the SMS technology, if Internet connection is not available and the message is small.

You can turn off the "Send as SMS" switch, if you only want to use iMessage and MMS technology.

The picture below shows you how to turn on SMS function on your iPhone:

⇒ Differentiate iMessage and MMS/SMS on iPhone

⇐ What Is SMS (Short Messaging Service)

⇑ Using Messages App on iPhone

⇑⇑ Apple iPhone - Frequently Asked Questions