^^^ yes there is difference between I9100 and I9100G
in i9100g the processor is under clocked to 1008 mhz, lower gpu, samsung claims that its battery backup is better...
i9100g doesnt support many games like asphalt 6, modern combat etc and may be some heavy apps(not sure about apps)...
even ics update is only for i9100 and not for i9100g.. so i will suggest u to go with i9100 or iphone..
more detailed comparison here..http://10division.com/samsung-galaxy-s2-gt-i9100-vs-gt-i9100g-ultimate-comparison-guide-all-you-need-to-know/
hope it helps...