Hangouts is the supposedly Googles answer to a unified messaging application but some are having difficulty install it on tablets, some on phone too.
If you are rooted and cannot wait to try this new application there is a simple way to install it in your Nexus 7 if you have toy access.
Firstly you need to uninstall Google Talk, this can be fine a number if ways but probably the easiest is with a free that many if you will have and that is of course Titanium Backup.
Simply tap on the Talk application, select uninstall and confirm twice.
Once this is done, open the Play store and search "Hangouts". Open the application page or tap the three periods and install.
Your done, you now have Google Hangouts.
It had been confirmed that eventually this will replace G+ messenger once all data has been migrated and is likely to include SMS messaging at a later date.
Sent from my Paranoid Nexus 4 using Tapatalk 4 Beta