Though iPhone OS 4's real potency will come when developers seize the new tools and build multitasking apps that do crazy, crazy things, many of the OS's inherent secrets are coming to light. Updated: More secrets.
Cellular Data On/Off
You now have the option to toggle cellular data off.
SMS Character Count
Guilty of running long on short messages? Now you can turn on a character count for SMS.
SMS Search
Just as you can search your inbox, you can now search SMS messages.
Home Screen Backgrounds
You can set separate backgrounds for your lock screen and home screen.
Camera Zoom
By tapping the screen or sliding the little bar, you can zoom in and out when taking a picture.
Web and Wikipedia Search
Can't find what you need on the phone? Jump to the Web or Wikipedia straight from the global search screen.
Streamlined "New Contact" Screen
You can now enter more contact data without leaving the main screen. When you consider that every green plus signifies an annoying jump to another screen, you can easily see how much better it is now.
Art in Album View
When you browse albums, and find one you like, you get more than just a list of tracks and a shuffle command. You get a little thumbnail of the album itself, and the length, track count and release date.
App-Specific Location Services
By heading to Settings > Location Services, you'll be able to toggle which apps you're allowing to find your location and see which ones used the privilege recently based on the little compass arrow icon next to them.
