Tata Docomo is the cheapest mobile operator in india. Their plans are very cheap among all other operators but their services are not good. Their customer support is not good. Coverage of tata docomo is good in my area. Both 2g and 3g signals are good but in village the coverage is worst. Whenever I was travelling there is no signal in my mobile. This is the worst thing.
Tata docomo is only good for urban areas not for rural. Their internet packs are awesome but speed is not that great. Sometimes I have to disconnect internet and reconnect. This is not good. Day time speed is superb but at night it becames slow. I mostly uses 3g. Their * 123# offers are awesome. So I would suggest u that if u lives in urban area then go for docomo but if u lives in rural area choose other operator.