Personally, I don’t install custom modem on my Samsung Galaxy S III. I will stick with the modem (radio / baseband) that comes along with the firmware unless the modem is highly recommended by others. So have to install official custom modem on your Samsung Galaxy S3 manually. What is the benefit of using custom modem? Using the correct modem will give your Samsung Galaxy S3 better signal coverage, reception, speed and battery life. Choosing the correct modem take time. You need to benchmark the 3G speed, battery consumption, signal strength… Monitor its performance for days. So I don’t change modem much unless I found the one that I am using is bad.
Official Samsung Galaxy S3 modem
How to install custom modem on Samsung Galaxy S3?
There are several ways to install custom modem on Samsung Galaxy S3 ~ Odin, ClockworkMod Recovery (CWM) and kitchen (on custom ROM like CheckROM).
Use Odin to install modem tar (or tar.md5) file. Just like the way to install CF-Root kernel except you put the modem file at PHONE instead of PDA in Odin.
If the modem is in CWM zip flash-able format, ClockworkMod Recovery is the tool that will help you to install the custom modem. Refer How to install update zip with ClockworkMod Recovery on Samsung Galaxy S3? (Video) guide to more information.
Finally, the easiest way ~ using KitchenPro App in CheckROM. Just mark the modem that you want for installation. Then Apply it to install. That’s all.
Download official Samsung Galaxy S3 modem here.