Sorry for the delay in responding. Here are the basics on the texting feature.
1. Go to Voice Choice settings and choose the preferred texting app other than Google Voice (the texting app used to send text messages with your cell phone number)
2. Initiate a text message in some preferred manner (perhaps a "Direct Message" widget on your home screen3. *If you haven't yet designated an Android system wide default app for sending text messages, you'll get a list of all apps capable of sending texts. Voice Choice should be one of them. Select it and make it the system wide default ("Use Always" or something similar)
4. Voice Choice will examine the number and check to see if Google Voice's compose window should be launched or if the other texting app's compose window should be launched.
*If you have already designated an Android system default app other than Voice Choice, go into Android settings, remove the default, and go back to step 2.
Let me know if that all makes sense.
-Kevin