Google Hangouts for Android has released its new version 2.0 which has SMS/MMS integration (Supports on Android 4.0+ devices). After the update you will be prompted to enable the SMS in to Hangouts or you can also try it later. You have integrated the SMS into Hangouts and if later you want disable the SMS integration from hangouts we have a tip for that.
How To Steps:
On Android devices which is running Android OS version 4.4,
1. Go To Settings -> SMS
2. Then Click on the “SMS Enabled” feature to change your default SMS App.
On Android devices which is running Android OS version 4.3 and on its lower versions,
1. Go To Settings -> SMS.
2. Then uncheck the box next to “Turn on SMS” to disable the SMS integration from Hangouts.