Actually, this could be very useful, if it were to be handled well enough.
I mean, yeah, you can call and hangup and they'll send everything, but in, say, a situation where you don't need everything (like, most situations), they could set up a basic code system.
So, for example, you enter 911 in the texting area, the phone immediately becomes silent, you enter a series of very simple menus to indicate to the receiver what needs to be sent and how much of it needs to be sent (so they don't send special forces to a mugging), and then an optional field for a description of the case, if the sender has the ability to describe it. Then the text goes off to emergency response center, they can figure out where the phone is pretty quickly on their computers (I assume they can, I don't see why they couldn't, I mean, they should be able to triangulate the location from phone towers in the area, right?), and appropriate emergency services, not an all-out thing that would be sent on a hang-up, can be dispatched.
This would allow for somewhat specific calls for help to be sent in a very small amount of time, and they would be completely silent as well.
