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In previous versions of the OS, you had to open a note and tap on the trashcan icon to delete it. You can now swipe across an item in your Notes list (from left to right, or right to left) to display a Delete button.

It’s easy to lose track of how many third-party apps you’ve installed on your iPhone. With OS 3.0, you can find out quickly. Go to Settings >General >About and look at the list. It will tell you the network you are connected to and the number of songs, videos, and photos you have on your device. The fifth item in the list tells you how many third-party apps you have installed.

The new Spotlight search feature can be accessed directly from other apps. 

Spotlight Search is one the best new features in OS 3.0. Given that you can now have up to 11 pages of apps, swiping constantly to find them can be a bit irritating. Spotlight Search is the fastest way to find an app, contact, e-mail, song, video, or other piece of data. Simply open the Spotlight Search window, begin entering your search query, and a list of possible results is displayed and refined as you type. When you see what you’re looking for, tap on it to open it.

OS 3.0 adds Cut, Copy, & Paste capability to the iPhone and iPod touch. This system-wide feature works with any app that accepts text entry. Before you can cut or copy text, you first have to select it. To do this you have to do the following:

I have some news that should resolve the overheating issue that has been plaguing a percentage of iPhone 3GS owners since its release. I have not experienced this issue myself, but have a very reliable source who has and who claims to have solved it. It apparently has to do with a corrupt software image of OS 3.0 that was flashed onto the devices during production.