You need to go into Settings>Applications>Manage Applications>Messaging and clear out the defaults on the stock messaging app. Then, the next time you try to text someone from Contacts, you'll get a box asking which one you want to use, Google Voice or Messaging.
Nope. Under the "launch by default", it's all grayed out. At least for me. Anyone else get something different?
I've been trying to get GV to be my default messaging app for some time, but it's just not possible. I would LOVE to use the new Google Voice Search to send texts, but it always starts up my regular messaging program rather than GV.
Everytime I want to send a text, I have to manually open the GV app and sent it through there. And I'm not sure what some people are talking about here, I get it all in a nice threaded format.