I have sent probably 10 pictures today without an issue (Sprint Arrive) so its not Mango or Sprint unless its something with your account. Is your WIFI turned off? Maybe that's it or a signal issue. When I have a bad signal I get that error but in the text message there is a place where it says try again I just go to a place with better signal then tap try again and it works fine.
I add text all the time no issues. I start in camera roll chose send from the 3 dot menu then messaging then chose who to send to. Add text at the bottom of the picture in the text box and send