Why am I not receiving messages on my iPhone?

[iMore Question]

When text my text bubble is green when it should be blue

 

[kch50428]

The person on the other end may not be/is no longer using an iPhone.

 

[Just_Me_D]

If you know for certain that someone has sent you a text message (SMS) that you've yet to receive, notify your wireless carrier to have them troubleshoot from their end.