TATA DOCOMO in its starting phase was one of the best telecom company in India, and its been degrading ever since. Data speeds are abysmal. Network coverage is quite OK.
But, it is not supported in all the states while is a huge let down for example there is no tata docomo in Delhi or Noida. So better look-up before changing.
Data rates are OK compared to other vendors but speed is really not up to the mark.
Call rates are no better than the others.