When Google killed Google Talk in favour of Hangouts, many expected the company to merge all its various communication services under the Hangouts umbrella. Sadly, it took Google more than 6 months after Hangouts was released to even bring half-baked SMS integration to the app.
Google has also promised Voice users in the States that it will eventually integrate Google Voice to Hangouts but this will take its own sweet time. Beating Google to this feature is Koushik Dutta a.k.a Koush from the CyanogenMod team. Koush has managed to integrate Google Voice with the Hangouts app using his Voice+ app.
The Voice+ app is a part of the CyanogenMod ROM, and will allow users to send and receive messages using Google Voice. Voice+ earlier allowed CyanogenMod users to send and receive texts from Google Voice via third party messaging apps. This feature won’t be available to stock ROMs or by side-loading the Voice+ APK on the stock ROM, since enabling this feature requires some underlying framework modifications.
It is unclear whether this feature will only be available in CM11, based on Android 4.4 KitKat, or will also be backported to CM10.2. This new feature has not yet made it to the latest CM nightlies, but that should happen soon enough!