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.