Apple is still busy demonstrating the new features of iPhone OS 3.0 at WWDC. Here are some of the key features:

iPhone OS 3.0 brings over 100 new features
MMS support
Search – calendar, music, e-mails and notes
Spotlight – universal search including apps
iTunes to allow buying movies, music, TV shows and audio books over 3G. (Alas, the iTunes Store is not yet available in India.)
Parental controls
Tethering! Allows you to tether your iPhone to a laptop/desktop using USB or Bluetooth to connect to the Internet. Only 22 carriers support this feature, Bharti Airtel and Vodafone are on the list! Yippee!
Audio and video streaming over HTTP
Auto-fill support for web pages as well as HTML5 support
More than 30 languages supported by iPhone OS 3.0
Find my iPhone feature, if you lose your phone – only for MobileMe subscribers. You can even wipe all data from the phone.
In app purchase