I am a customer of Aircel from 2003 and for the past 5 years and it has not let me down even a single day. Their tariff is the lowest in the market both for Postpaid & Prepaid. But one should avoid Postpaid and go for Prepaid connection, because they ask for deposit for STD & ISD. Also it is very difficult to get refund of deposit if you want to close the connection.With Prepaid one can make any call without any security deposit.
I have travelled to Kerala, Karnataka and Mumbai with this SIM and roaming network is also good
I find many times whenever I dial a BSNL mobile number the call does not go through .But if I dial the same number(BSNL Mobile) through a BSNL Land Line the call gets connected. I think they are puposely doing this to increase
their revenue.
I think Airtel has the costliest tariff and a average network. BSNL, Vodaphone are OK tariff wise but network coverage is not as good as Aircel
So if you are in Chennai or Tamilnadu go for Aircel Mobile for trouble free service