There is a way to use Picture MMS on the Sprint service, but it rather a bit drawn out.
First thing that needs to be done is to activate the sprint Pic Mail Service. You must set up a pic mail email and have it link to your phone. Eg.
So once that is done, when ever you take a picture email it to yourself (at your pic mail service) then sprint will text the picture to you, and from here all you must do is forward it to who ever you like.