I’m with TATA Docomo since Feb 2011. Billing is perfect, no mistakes, rare unknown deductions.
problems
Network coverage - you are zero when you leave cities, and I used to get at least 2-3 SMS alerts which says I had missed call when I was fully in the network.
Customer care - either they have employed poor quality executives or they have outsourced it to some cheap companies. both ways, they are responsible, they hardly recognize our problems and they never respond. even for emails. though the highest resolution authority needs a push to reply for emails.