My mother (S4 Mini) was unable to receive texts from me (S3) for a few days. I could get all of her texts and there were no issues with calls. Solution: Turns out my messages were being interpreted as spam. Go into Messages, press the menu button, and go to Spam Messages. Every contact listed there is being blocked by your phone. Go back to Messages, press menu again, and enter Settings. Scroll down and uncheck Spam Settings. This worked for us.