Q:

Mass confusion about present and future: Hangouts, SMS, MMS, and Google Voice

I've been trying to make sense of recent news and theories about the future of Hangouts, SMS/MMS integration, and merging with Google Voice. 
My main concern right now is that I want to continue having free SMS messages sent through my Google Voice number. I don't have any texting plan from my phone company -- my "real" number is secret to the world. 
The facts:

I have a Google Voice number that is public, for calling and free texting
I have a secret "actual" Verizon phone number, SMS or MMS costs $0.25 per message
Google Voice doesn't support MMS
I do not want to activate SMS over Hangouts because I fear it will use my Verizon number which does not have free texting

Am I correct in my concerns? Should I hold off activating SMS in Hangouts because I will end up with a lot of fees from my carrier? Should I pay for an unlimited texting plan with Verizon because doing all of these things won't be free in the future anyway?

Google Hangouts + Voice Integration
Update Sept 10, 2014:  Google has now merged Google Voice into Hangouts. 

A:

If you keep using the Google Voice app for texting, it doesn't matter if you activate SMS via Hangouts.  However, any texts you send out of Hangouts will go through your Verizon number, incurring carrier charges.
If you are running CyanogenMod 11 ROM, you may want to look into Voice+.  It's a custom app that allows you to pipe all "regular" SMS through Google Voice, from any app such as Hangouts, Messaging, HandCent, Whatsapp, etc.  It's still in beta (as is the entire CM11) but works quite well for keeping all the messaging together in a single app.
When Hangouts got ability to send/receive SMS last year, Google promised that they will eventually merge Google Voice functionality into it, thus making it a single app.  This looks to be slowly happening behind the curtains. In the latest Hangouts v2.1 update, bits and pieces pointing to Google Voice integration started showing up.  We will most likely hear more about this in the upcoming Google I/O developers conference this coming Summer.

