Install the ROM ZIP and a corresponding "GApps" (Google Apps) package to regain access to the Play Store and other Google services.
This guide is strictly for the international GT-I9100 . Do NOT use these files on the GT-I9100G , AT&T, or T-Mobile variants, as their internal processors differ and flashing will permanently damage the hardware. Verify your model by going to Settings > About Phone . gti9100 firmware 511 download upd