If you are a Vodafone customer and you buy a Samsung Galaxy S2, you can get Free 1Gb/Month 3G/2G data transfer for 6 months. When you start using your Vodafone Sim in your Samsung Galaxy S2, the request will be registered automatically, and will get activated with in 48 hours.
This is listed in the official website here - http://www.samsung.com/in/galaxys2/. If you want to know more about it, better you call and talk to Vodefone Care. This offer ends on 31st August and not available in Jammu and Kashmir, says the disclaimer.
It is activated on my phone.
Samsung Galaxy S2 features
4.3 Inch SUPER AMOLED Plus display
1.2 Ghz Dual core Processor
16GB internal memory
Android 2.3 (Gingerbread)
And more. I have purchased it 14 days before and so far am satisfied with the performance. Am not a Android expert, trying to learn more about it btw.