Disclaimer: I don't have a Droid yet.
I've read where Google Talk is the same thing as instant messaging so you can converse with others that have downloaded Google Talk as well. So yes, this would be the same as free text messaging, but you would not be able to send pictures that way. I'd opt for email in that case as a workaround. Good luck.
Google Talk IS NOT GOOGLE VOICE
Google talk is just instant messaging.
The OP is asking about SMS via Google Voice.
THe general consensus is YES if you use the Google Voice App to send/receive SMS exclusively you will have unlimited txt messages.
This is dependant on how you have your Google voice & Verizon account set up though.
I would recommend under google voice settings on your computer to make sure the check box to COPY SMS TO THIS DEVICE is unchecked, in addition to calling up verizon and asking to block all SMS TXT messages. After you do all of that you should be able to strictly use Google Voice and not have it reflected on your Verizon service at all.