Apple Iphone 3G activation Airtel

First you have to get activated 3g services on your sim and then perform the following steps

Enable 3G and celluar data
Settings -> General -> Network
Enable 3G – On
Cellular Data – On
Data Roaming – On (Optional)
Reset Network Settings
Settings -> General -> Reset
Reset Network Settings
The Iphone will restart and u r ready to browse wit Airtel 3G