With the release of iOS 5, Apple has added the ability to buy custom alert tones from the iTunes app on your device. If you open iTunes and click on Genres, you will see a new entry called Tones.
The iTunes Store on your iPhone, iPad, or iPod touch now includes the Tone Store — an incredible spectrum of music ringtones and alert tones that can be assigned to any alert setting on your iPhone, iPad, or iPod touch.
We already knew about Ringtones but these alerts are a completely new feature. Some of the Star Wars alerts are particularly impressive and comprehensive too. Alerts will cost $0.99 whilst Ringtones still cost $1.29. You can also access the Ringtones and Alerts directly from the Sounds tab within the settings app.