Set up your mobile phone for iMessaging
You can send iMessages to phone numbers or email addresses if the recipient has a device that supports iMessage. Before you can set up your mobile phone for iMessaging, you need to activate your Apple ID.
Turn on iMessage
Tap the indicator next to "iMessage" to turn on the function.
Turn SMS alternative on or off
Tap the indicator next to "Send as SMS" to turn the function on or off.
If you turn on the function, your iMessages will be sent as SMS if the service is unavailable.
Return to the home screen
Tap the Home key to return to the home screen.