Wait - is this a prank? The S5 really doesn't have that capability and it was sold to Sprint customers without that information being made clear up front? Will it ever have that capability? Is this why I have to turn my wifi off in order to send and receive picture texts as well? Wow, I feel like I got scammed a bit here..
US carriers are switching to phones with one Antenna in them (voice and data over LTE), at the moment that will limit the capabilities of the phone to talk and surf in the same time, other carriers have started (3-4 cities that I know) and Sprint is about to start turning on this capability but it will be a while until the whole US will be able to do that.
Pictures use Data, so if you are not under WiFi, you will not be able to talk and send a pic message.