Well as I know bpl is one of the first mobile service provider in india.I was a tata indicom user 2 months ago my first phone was tata ace 2 years incoming but I planed to change so I tool samsung c210 and a bpl card.
I took bpl as it seems to have cheapest flat call rates 1p/sec for gsm mobile(Yes only GSM mobile tata n relience are supposed to be landline its a surprizing thing for me also) and 2p/sec for ll n std 2.75rs/min well std isnt cheap but gsm calls are very cheap(though 30 paise connectivity charges are there n 80 paise for outside zone so 1st call is always expensive but not so much)
So call rates are cheap.Other very good thing about bpl is its recharg vouchers from 10-198 its really zoom(GF ko I luv u bolana he 10 ka choa recharg I too use it always)And other thing 25 paise sms(at the daily deduction of 1 rs only n it doesnt get deducted when u dont have any balance)
Other majour advantage is sms free offer I am owning a card which has 2000 local/natinal sms free for 6 months(it really helps me a lot)
Recharg(validity) are a very good thing here options are
rs validity talktime specialoffer
200 30 50 no
300 30 165 200 sms free
400 30 365 200/300 sms free
700 60 640 500 sms free
amazing na I heard hat latest offer is rs 650 recharg 1000 talk time n 90 days validity(not sure abt this one)
another good feature that for caller tune n downloading ringtones(mono), wallpapers, logos costs only 2rs/messege.
Now downsides
1)Poor n/w covrage
2)No GPRS in maharshtra(except mumbai may be)
3)No MMS
4)No sim card services like airtel live
5)Customer care costs 1rs/min
6)No other card types available like twin, one, frnz etc
But overall u do much calling n a long talking also then BPL rocks really.