How do I make Google Voice the default text messenger?

I've been hunting, searching, and poking around the menus on my Cricket Ascend, and can't figure out how to make the messenger default to GV instead of my cell number. My phone dials with GV as the default, it only seems logical there would be a way to do that for text too. My main goal is to keep my cell number hidden, instead of accidentally sending it out (like I have a couple times now.)

When I open the default messenger app, there's an option in the menu for SMS center number (which is set to unknown.) I'm not sure what it's for, though. Do I put my GV number in there?

edit: Ok, it won't let me put my GV number as the SMS center number.