Go to the left screen and touch "Go to all setting" > "Accounts & Synch" > at the top you will see the on/off toggle and turn it off. Then I setup these two smart actions on our phones:
1. Trigger - Display Status (Off)
Actions - Mobile data (Off) <--you can still get text and phone calls but know that once you turn on your screen you may have to wait about 5 seconds for the data part to come back on.
2. Trigger - Location (My house)
Actions - WIFI (On) <-- to counter this one I downloaded an app called WIFI Powersaver to turn WIFI back off after one minute of not being connected like for when I leave home.
I used to use Y5 Battery saver app to do the same thing but it didn't seem to work right on this phone so I found this alternative.
Also, if you didn't see it already you can turn off the 4G and turn on 3G, by downloading the "Phone Info" app. Open the app and select the CDMA auto (PRL). Just like
THIS LINK describes.