More or less all are same in terms of costing while voice call...
AirTel is though really cheap when it comes to Internet with High speed...
How ever at Kolkata
BSNL Manik Jod seems to be the cheapest when as a student you need a phone just to receive calls and to comunicate with your home
.. It comes free if you have any BSNL Landline
no rental how ever post paid...
I personally use Hutch or rather vodafone... reason for going to hutch 7 years ago was the network they have that time, it was the strongest in Kolkata, but in recent times afater vodafone took control the network is givving issues
I am a pre-paid customer, I recharge my number with Rs. 400/- which gives me Validity of 1 year
and each month I recharge with Rs. 89/- top up, which allows me to make Hutch to Htcu (Kolkata and WB circle) at Rs. 0.30/- pm (night Rs. 0.15/- pm), others any local @ Rs. 0.75/- pm and 300 Local SMS free
rest I have to use the Chota Recharge
but if you look my Hutch plan in kolkata you may find AirTel / Reliane GSM or CDMA / or any other operator has same kind of plan in same pricing