There are more than 1,000 new APIs in the iPhone SDK for iPhone OS 3.0, many of which enable iPhone/iPod touch to work with hardware accessories that we’ll be seeing more of in the future.
Improvements in the iPhone SDK for iPhone OS 3.0 include:
In-App Purchase, which will enable you to sell content and services from within your app. Handles transactions with iTunes
Push Notification service means you can give your customers new info, notifications, or alerts even when the app isn’t running.
Accessories— Applications can now communicate with your accessories through either a dock connector or Bluetooth. An app can retrieve data from accessories or you can control accessories from the interface.
Peer to Peer Connectivity now applications, (not only games) can communicate via Bluetooth between devices. Game Kit supports voice communication from within apps.
The Map Kit framework lets you embed maps within your applications. Uses Google’s Mobile Maps with current location and geocoding, etc.
iPod Library Access lets you access a user’s audio library (music, audio books, podcasts) from your app with a new Media Player framework.