Being a customer of Excel - pre-paid mobile service of BSNL (Bharat Sanchar Nigam Ltd.) for the past 1.5 years I have got good amount of information to present to you about the service. As I have also tried Airtel and Hutch for short periods.
I will go in pros first:
Cost effective: Roaming cost and long distance calls (STD/ISD) are the best priced things with BSNL.
The recharge coupan: if u take that of worth 3000.00 or 2000.00 u get full talk time (there is no service charge) plus it goes for one year for 3000.00/6 months for 2000.00. So even if u are spending less then 300 Rs per month on phone, u have nothing to loose.
They don’t send you 10 SMSs per day with details of there schemes or to make you download ringtones and all absurd things:-)
There is no hidden charge as in Airtel or hutch. (Airtel/Hutch will deduct Rs1 or 2 per day for some plans , which you will never use in normal cases)
Coverage: I travel and at no point I am disconnected. Thats the best thing about BSNL.
Cons
Customer care is good for nothing!!
Earlier they had a 15 second pulse....no more(now its 1 minute)
Difficult to find details about their schemes
Difficult to get a prepaid card(Excel)
Overall good to have. Cause you want a simple card that allows you to make calls and receive calls at cheapest rates.