So you own the latest smart phone beast, the HTC Thunderbolt, but you don't get 4G service in your area yet and it's killing your battery life because of the constant 4G searching. What to do? The 4G network is spreading throughout the country which is great, but it's not provided in your area or you've traveled to a non-4G destination. Why not turn off the 4G and save battery life? Turning off the 4G on your HTC Thunderbolt is very easy to do and the procedure is reversible.
Step 1 Dial in the code for the hidden menu.
Start by dialing *#*#4636#*#*.
This will automatically enter you into the hidden menu. There's no need to hit send.
The hidden menu will pop up.
Step 2 Select Phone information.
Simply click on Phone information. This will bring you to the next screen (Phone information).
Step 3 Change to 3G Mode only.
Now scroll down until you see CDMA + LTE/EvDo auto. Click on it and change it to CDMA auto (PRL).
Picture of my phone has already been changed to CDMA auto (PRL).
You will see the following pop-up menu when you click on the CDMA drop down button.
Once you've selected CDMA auto (PRL), back out of everything by clicking the back arrow on your phone (next to the menu button on the bottom of the phone).
Your phone is now running on 3G only and you will notice battery life improvement. Want to turn it back on? Simply repeat the steps and select CDMA + LTE/EvDo auto. Enjoy!