Solution 4 of 4: Your phone hasn't been correctly set up for iMessaging
You can send iMessages to phone numbers or email addresses if the recipient has a device which supports iMessage. To set up your phone for iMessaging, you need to activate your Apple ID.
Step 1 of 5
Press Settings.
Step 2 of 5
Press Messages.
Step 3 of 5
Press the indicator next to "iMessage" to turn on the function.
Step 4 of 5
Press the indicator next to "Send as SMS" to turn the function on or off.
Step 5 of 5
Slide your finger upwards starting from the bottom of the screen to return to the home screen.