Vodafone is one of the major mobile network services in India providing good consistent network for their customers. I have been using vodafone since 2 years in Chennai and I must admit that no other networks would have given me such a good service in Chennai.
Initially I was a prepaid customer for vodafone, but their postpaid have much better plans and yes it saves a lot of money compared to prepaid. coming to their network signals even though I work 22 kms far from Chennai I do get a better HSDPA signals (3G Signals)
Internet speeds are much better in 3G compared to 2G speeds, 2G fluctuates and lags with low speeds. I preferred 599 plan which does my monthly job pretty easily with local std & data plan. Overall I think vodafone is one of the best networks in India and I do recommend it for my friends.
Biggest Cons & Point to be Noted: Their Customer Service is pathetic!