Australian carrier Telstra scheduled an Android 4.1.2 Jelly Bean update for Samsung Galaxy S III 3G on February 4. However, the update was pulled for unknown reasons and without any further notices.
The good news is Telstra is now back with the update and AusDroid reports some users already reported they have been able to upgrade to Android 4.1.2 Jelly Bean platform.
According to the latest hearsay, this Jelly Bean update is pushed OTA (over the air) in waves, so not all Samsung Galaxy S III 3G owners will receive it at the same time.
Those who have yet to be notified on the update can check for it manually by going to Settings / About phone / Software update / Check now. Keep in mind that you can also grab this upgrade via Samsung Kies desktop software.