I have earlier used
Tata DOCOMO GSM unlimited plan some 3 to 4 years back (before switching to airtel). Their onnet free unlimited roaming is as good as useless as phone latches to idea or Vodafone network at the fall of the hat. To add insult to the injury, they have started switching off the less used towers.
If used manual selection of Tata DOCOMO network, I have started missing calls due to worst in building coverage. Later they also started charging for missed call alert as if their network is world class (even now airtel and bsnl is providing the missed call alert service for free, even though their network is good).
Tata has taken all the worst decisions in telecom.
{1} First they didn't allow foreign handset usage in their cdma network and priced their own useless phone for ridiculously high price.
{2} Next they stated concentrating on GSM network with relatively bad spectrum and neglects cdma with good spectrum. Yes, they started to cover more towns for GSM network, while cdma network was left as it is.
{3} Later they have good cheap 2g data packs in GSM docomo, but uselessly costly data packs in cdma indicom (actually cdma handles 2g data better imho).
{4} Then they started switching off cdma towers in small towns and villages. At this point, I have to port out to their GSM network, as my in-laws town is one of them, with hope that they will improve their GSM network + I can use Aircel TN network (has better coverage than airtel here) with no extra charge.
{5} But later they started neglecting GSM networks too. It's almost impossible to complete even a 10 sec call in running train. Later I have ported all those 15 plus Corp connections with fancy numbers to airtel and living peacefully then.
Tata has the best tariff plans with worst network afaik. But this tariff is not even good as their earlier plans, imho.