The best free 3G data pack currently available in West Bengal & Sikkim is the 3G Mobile Unlimited Data Pack 1099 costing you just 1099.0 at the rate of Unlimited. from BSNL for 2 months.
Compare it to the best free 3G night data pack available in West Bengal & Sikkim from Vodafone is the 3G/4G Data Pack 29 which costs 29.0 and offers Unlimited. for Less than a month.