I own a Samsung Galaxy S2 (GT I9100) and few days back one of my friend bought a Samsung Galaxy S2 (GT I9100G). Samsung introduced the I9100G silently in to the indian markets due to the high demand for the Samsung Galaxy S2.
The main difference between I9100 and I9100G is they have totally different Processors , I9100 have Exynos Processor while I9100G have OMAP 4430. Also the for graphics support I9100 have ARM Mali 400 MP GPU while I9100G have PowerVR SGX 540 at 304 GPU.
1) Graphical Support
SII I9100G - PowerVR SGX540 (300Mhz) - Single core
SII I9100 - Mali400 GPU (400MHz) - Quad Core
2) 3G data rates
SII I9100G -> 7.2 Mbps HSDPA; 2 Mbps HSUPA - same as in older Nexus S (single core GPU)
SII I9100 -> 21 Mbps HSDPA; 5.76 Mbps HSUPA - Quad core GPU
3) Operating frequency options
SII I9100G -> GSM - 900, 1800; UMTS - 2100
SII I9100 -> GSM - 850, 900, 1800, 1900; UMTS - 2100
(It means I9100G can't use while travelling out of India)
SII I9100G - 1.2 GHz, OMAP 4430 (Will reach a maximum of 1008MHz)
SII I9100 -> 1.2 GHz, Exynos 4210
5. It is expected that all new updates (Like ICS Android 4.0) will be available for I9100 earlier than I9100G.
So Before you purchase a Samsung Galaxy S2 from Asia (Mainly from India)
1. Make sure which model you are going to get, I9100 or I9100G
2. Find the difference and decide which phone you want to buy I9100 or I9100G.
Read a discussion on XDA Developers
Reviews on Flipkart