Can't text photos to another iPhone

I have had an iPhone 4 (sprin iOS6) for over 2 years and had no problem texing photos to anyone. I noticed yesterday I cannot text photos to another iPhone although they will go to an Android. I CAN get photos from another iPhone.

All the settings are correct, nothing changed. I have done the following.

1. I turned MMS off and on

2. Turned my phone on and off

3. Turned airport on and off

4. Reset Wifi connection

What is going on and how do I fix it?

Thanks