While I would post the instructions to activate, settings, and connection details later, here is a summary of my experience.

Speed
I get a decent browsing speed when in Chennai. Way better than a dial-up.
However, in other parts of Tamilnadu, the speed is quite low. I guess the reason is EDGE support in Chennai, which is only available in select cities.

Download speed is typically 50 kbps to 100 kbps (Kilobits per second) – transfer 6 to 14 KBps ( KiloBytes per second )

Downloading this document took 18 seconds. It’s hosted on a server in India.

Plans
Airtel postpaid plans ARE costly for GPRS. Like GPRS plans of most
providers, they are data usage based.
There are three plans with postpaid.

1. Rs. 399 /month – 100 MB free – Rs. 5 for every MB beyond free usage
   • This plan is completely suitable only if you’re going to do occasional mail checking.
2. Rs. 599 /month – 1 GB free – Rs. 3 for every MB beyond free usage
   • Costly. But worth using for most business purposes
3. Rs. 799 /month – 1.5 GB free – Rs. 3 for every MB beyond free usage
   • Just a number play. I think Rs. 599 is more worthy, compared to this plan.

I used Mobile Office – Rs. 599 plan

Usage
I got it working with Linux. Here is what I used as of this writing.

• the excellent HP dv6000 series laptop.
• Kubuntu 7.10 (beta)
• kdebluetooth ( and pppd )
• Sony
  Ericsson W300i
• Airtel mobile office Rs. 599 plan ( post paid )

When you’re connected to the internet, you would seem “Unreachable” to other people trying to call you. However, if your internet connection is idle, or you’re not transmitting lot of data, you might receive a call.
If you receive a call your internet connection stops. It resumes internet connection once you hang-up.

Summary
If you need internet connectivity when mobile – traveling , to use in the car (assuming someone else is driving) you could very well consider Airtel GPRS. You would need a EDGE compatible cell phone. If you can’t get EDGE support in your city, I don’t think it’s worth using this plan.