Ron Amadeo of Android Authority has ported some nice APKs from Google Nexus 4 Android 4.4 KIT KAT for non Android 4.4 smart phones. First of the APKs is Google Hangouts v2.0 with SMS/MMS integration into the one messaging App which will combine Google Hangout Chats, SMS, MMS and IM into one.
You can download the Google Hangouts v2.0 APK here. After installing it turn on SMS in the settings you will have both the Google Hangout Chats and SMS in one place. A small icon on each conversation's profile picture will alert you if the message is an SMS. Swiping to the side will archive messages (retrievable from the Settings menu).
The other APKs posted by RON Amadeo are as follows :