If your phone is listing the image as sent, but the windows phone is saying the image is too big, and the iphone is not getting it at all, it sounds like it's an issue with your friends' phones and not yours. When my fiance and I both had blackberries we used to send images to each other constantly, but as soon as she switched to a galaxy it stopped recieving, so as far as I know, some phones don't like getting images through texts.
That's just my guess though, I could be wrong.
