Using Google voice number without data
I figured it out.  If you navigate to this page, and tick the receive text messages on this phone box all texts to Google voice will be forwarded to your phone via SMS.  This generates a new number for each of your contacts that will travel between Google voice before delivery, making it so you will always show as your Google voice number to friends, even if you are outside of wifi.  So just need to save the new number for each contact and be sure to text that instead of their actual number and it works perfect.  More info here.