Please note this phone is capable of 1X only at this time.
Install Drivers for Samsung Galaxy S3
Android 4.1.2 Open Dial Pad
At Hidden Menu Screen Select Hidden Menu
Select Enabled and Press OK
Next, press back to bring up the dial pad.
Select Qualcomm USB Settings
Select DM + MODEM + ADB or RNDIS + DM + MODEM
Press Back Till Phone Is At Home Screen
Phone Is Ready To Be Provisioned
(Remember after flashing to return and put phone back to MTP+ADB)
Open the dial pad
Enable DM Mode