most, if not all, modern cell phone does have an "email address" for their phone...instead of them putting in your phone number, they, believe it or not, can actuually type in an email address, when they do this and it sent to you, you can actually see their cell phone's email address...when you want to send them a picture, you email the picture to that email address and they will get it as if it was a regular picture message
example: verizon wireless cell phones are 9998881234@vzwpix.com