Thanks for the great solution. It's working alright from me now. I have an idea connection and was struggling to get the GPRS through in my lumia 800. but I should say one thing. There were no issues like this with Vodafone sim.
any way thanks ad cheers.
For Airtel Gprs:
1.Set Access Point as airtelfun.com. It will connect to internet for some time.
2.Then Go to Market place and search "Network Application."
3.Download and Install the application.
4.Run the application.
It will autimatically detect the network as airtel for internet connectivity.
Now Browse to enjoy Mobile Internet.
If unable to connect to internet even after setting access point as airtelfun.com
Connect to wifi and follow the procedure from 2,3,4.
Super quick fix is just enable internet sharing option and ur 3g starts working fine...also uninstall network setup app...just use required apn