Just did a system update on Samsung Galaxy S3 (one that was sent by Sprint, I guess?). I am obviously not very tech savvy & don't know what the technical terms for everything is, so please bear with me! haha After the update, there is absolutely no 3g or 4g signal at all! Could the update turned some setting off that we can turn back on? Thank you!
Navigate to settings/connections/more networks/mobile networks.
From this screen Airplane Mode should be turned Off.
Next select Mobile Networks. The box to the right of Mobile Data should be checked and Network Mode should have the CDMA/LTE/EVDO preferred network mode selected.
Finally go to settings/connections/wifi and make sure wifi is turned Off. After wifi is turned off your phone will begin detecting the presence of a 3g/4g network. Once your phone successfully establishes a connection, you may go back into settings/connections/wifi and turn wifi back on.