A little hack found on the forums on about how to access the net from a pc using a mobile with Airtel prepaid card. Enjoy!
Raw Materials: PC/Laptop and necessary connectivity tools ,ie.,
Serial/USB cable OR Infrared Device OR Bluetooth dongle to connect the mobile to the computer.

1) Activate Airtel Live! ( It’s FREE so no probs)

2)Create TWO Airtel GPRS data accounts (yep TWO) and select the
FIRST as the active profile.

3) Connect your mobile to the PC (or Laptop) and install the driver for
your mobile’s modem.

4) Create a new dial-up connection using the NEW CONNECTION
WIZARD as follows

Connecting Device : Your mobile’s modem
ISP Name : Airtel (or anything you like)
Phone Number : *99***2#
Username and Password : blank

5) Configure your browser and download manager to use the proxy
100.1.200.99 and port 8080.( My advice is to use Opera since you
can browse both wap and regular websites)

6) Connect to the dial-up account. You will be connected at 115.2
kbps (but remember, that is a bad joke).

7) Pick up your mobile and try to access any site. You will get “Access
Denied…”(except for Airtel Live!). IT DOES NOT MATTER.
Keep the mobile down.

8 ) On the PC ( or Laptop) open your browser, enter any address ,
press ENTER and…….WAIT

9) After a few seconds the page will start to load and you have the
WHOLE internet at your disposal.