Sometime within the next two weeks, Nokia will launch the Lumia 620 in India for 15000Rs. I strongly recommend you purchase this mobile.
It has Facebook, Twitter and Xbox built in, plus the world's best maps. It also has Nokia Music - all-you-can-eat music mixes; you can download up to four of these mixes to listen offline, and there's no ads (absolutely free). It's a really fast, and smooth phone.
It comes in beautiful colours (lime-green, blue, black, yellow, white) with a great touchscreen - and it cuts down glare from the sun too. Finally, there is a 5MP camera and plenty of apps to download from the Windows Phone Store.
The 620 is also a far better device than the 710 because it has Windows Phone 8.
In comparison to the Galaxy S Duos, Lumia 620 has a clearer screen, double the amount of storage (8GB v 4GB - and supporting bigger microSD cards) and 720p video recording (versus VGA on the Galaxy)
It has a far better battery life than both Lumia 710 and Galaxy S Duos - especially for talk time. You can expect two days battery life with moderate usage.