I was a user of erstwhile SkyCell (Now AirTel) Pre-Paid Connection since July 2001. I was using the connection till February 03. The main reason I opted for this service provider was the 30 Second Pulse option that was given.
The service was really good (if you are not in one of the Bad Reception Areas, which are many). In these areas, you will definitely get a signal by sheer Magic, nothing else. I spoke to Customer Care so many times almost every day! (I had actually lost count). The reply I used to get was there was a problem with my Handset and that I should get my Handset checked. I have tried with 6 different handsets (Two of them had a problem), but even then, the reception is really bad. I hope they would have rectified them by now.
As far as the billing is concerned, What can I say? I was charged for SMS messages which were not delivered, inspite of the number being correct and receiving a Message Delivery Failed Report.
But the advantage I had with this provider was that they offered me STD and ISD facility without any deposit. I also had an option of free roaming across India (Except East at that time).
Inspite of all these problems, I would still recommend an AirTel connection to any user.
I am currently using a Post-Paid AirTel connection which is a part of a Corporate Group in Kolkata. Here I find that the Network is good and I have not used Customer Care till date. Also, I do not have any billing disputes. Which is better than what I had expected.