Sad news if you don't want Google(s goog) to consolidate all of your communications into Google Hangouts. A pair of recent developments strongly suggest that Google Voice is the next service to become part of Hangouts.
NDTV Gadgets noticed that Google updated its SMS for Hangouts support page with a note saying the service would be discontinued on July 2, which is today. This applies to the SMS for Hangouts on the web, not for the Hangouts app on mobile devices. If you want to use Hangouts for SMS, that option is still available.
However, there's also something going on with Hangouts for Android -- and possibly for iOS(s aapl) too, although there's no hard evidence of that just yet. A reddit user by the name of dude2k5 snapped a screenshot showing a Google Voice migration to Hangouts. The tool itself doesn't work yet, but it's a clear sign of where Google Voice is going: into the collective functions of Google Hangouts.
At last year's Google I/O event, Google suggested this might happen at some point in the future. In May 2013, Nikhyl Singhal, a product manager for all of Google's real-time communications services, specifically noted that "Hangouts is designed to be the future of Google Voice, and making/receiving phone calls is just the beginning. Future versions of Hangouts will integrate Google Voice more seamlessly."
It looks as if that future version with Google Voice integration will be here soon; I wouldn't be surprised to hear an official announcement before the end of this week, if not today.