The company often pushes out its iPhone patches at 10am PDT. UPDATE: It is available right now. iOS Firmware has links to the latest builds for direct download.
While you wait for the update to emerge (or to download), I thought you might be interested in this ten-minute video (via TiPB) which is a great little guide to the new features of the OS.
iOS 4.0 isn't compatible with the original iPhone or the iPod touch. iPhone 3G and second-gen iPhone touch devices will get the update, but key features will be missing.
The 2009 iPhone 3GS and current generation iPod touch will gain all the new features, including multitasking, folders, wallpapers, unified inbox, multiple Exchange accounts and more.
To get ready for the update, do ensure you've upgraded to Tunes 9.2 and make sure to update all your apps. A deluge of updated applications are beginning to slip inside the App Store.
Once this upgrade is complete and the first iPhone 4s begin reaching customers, Apple's next big moment will be the debut of iAds. The first placeholders for these are beginning to appear within some applications now, with more sure to follow.
Apple has quietly prepared the ground for the software upgrade. For example, within the iTunes 9.2 Devices menu the image of the iPhone has changed from a basic 3GS to a 3GS featuring the iOS4 wallpaper.
To get the update you must first connect your device to iTunes and follow the simple steps required.
Three key features will make this an upgrade worth racing for:
This isn't a complete multitasking solution, it requires your apps be multitasking-ready. Essentially in future (as updated apps appear) you'll be able to continue listening to music from within one app while working inside another. Though (sad to say), Skype -- which was a feature multitasking star at Apple's iPhone event earlier this year -- isn't yet ready for this feature. For shame.
The introduction of Folders means you'll be able to gather all your apps inside logical collections nested inside folders. With iOS4 you'll be able to group all your games together, or all your social networking apps. You can store up to 12 apps inside each folder.
Available for the iPad since that hit product reached the streets, iBooks will come to the iPhone. Better yet, when you close a book on your iPhone and then open it again on another device, such as an iPad, your bookmarks etc. will all be in the same place. Battle between Amazon and Apple for the eBook market is fierce, though Amazon has the best prices and a wider catalogue.
If you don't mind using an older iPhone -- albeit with new features -- the imminent iPhone 4 means now is probably a good time to search eBay for a bargain.
You should find some good deals on second-user iPhone 3GS units as people sell theirs to finance a new iPhone 4 purchase.
Upgrading your iPhone to the new OS is unlikely to be a completely smooth operation. Apple's servers will be hammered as millions of users attempt the upgrade. Patience is a virtue -- it will be easier to upgrade later this week.
(Upgrading later also helps avoid any last minute minor bugs that mayhave slipped through beta testing)