So far I know of no app I can use on my Android phone to let me send SMS showing my Google Voice number when I have no data plan (and no WiFi). However, if I have set up Google Voice to forward incoming SMS to my handset and I receive one, if I respond with text the original sender will receive the text from me showing my Google Voice number as the source. Whew!
Naturally, if I have an Android phone even with no active data plan but with live WiFi and I initiate an SMS it will show my Google Voice number as the source, depending on my settings...

Naturally, if I have an Android phone even with no active data plan but with live WiFi and I initiate an SMS it will show my Google Voice number as the source, depending on my settings...
