Google has announced on his blog that it is carried out Android 4.1 update for the Nexus S's T-Mobile, H3G, O2, Rogers and Vodafone in many different countries. More specifically, the Nexus S model is updated in this phase has number and i9020T i9023, i9023 which has frequently been the person chosen to use Vietnam. Google does not announce the specific time to upgrade to the Nexus S variants of each home network, but you can try to access the Settings> About Phone> Software Update to see if your machine has tasted marshmallows Jelly Bean or not mild. Jelly Bean is the Android version bring in their latest changes, such as Project Butter idle smoother, richer sound notification, Google Now, slight changes in the interface compared to Android 4.0. .. You can see more details in new features article on Jelly Bean.
According to the Google Blog, GottaBeMobile