The wait seemed eternal but we are getting reports that Apple has finally started rolling out iOS 4 - its eagerly-awaited next generation iOS.

Apple had given us a sneak peak of its next generation iPhone OS in April. iOS 4 includes over 100 new features for iPhone users and more than 1500 new APIs for app developers.

According to the release notes iOS 4 includes the large list of new features:

• Multitasking support for third-party apps* – Multitasking user interface to quickly move between apps – Support for audio apps to play in the background – VoIP apps can receive and maintain calls in the background or when device is asleep – Apps can monitor location and take action while running in the background – Alerts and messages can be pushed to apps using push and local notifications – Apps can complete tasks in the background 

• Folders to better organize and access apps 

• Home screen Wallpaper* 

• Mail improvements – Unified inbox to view emails from all accounts in one place – Fast inbox switching to quickly switch between different email accounts – Threaded messages to view multiple emails from the same conversation – Attachments can be opened with compatible third- party apps – Search results can now be filed or deleted – Option to select size of photo attachments – Messages in the Outbox can be edited or deleted 

• Support for iBooks and iBookstore (available from the App Store) • Photo and Camera improvements – 5x digital zoom when taking a photo** – Tap to focus during video recording** – Ability to sync Faces from iPhoto – Geo-tagged photos appear on a map in Photos 

• Ability to create and edit playlists on device 

• Calendar invitations can be sent and accepted wirelessly with supported CalDAV servers 

• Support for MobileMe calendar sharing 

• Suggestions and recent searches appear during a web search 

• Searchable SMS/MMS messages** 

• Spotlight search can be continued on web and Wikipedia 

• Enhanced location privacy – New Location Services icon in the status bar – Indication of which apps have requested your location in the last 24 hours – Location Services can be toggled on or off for individual apps 

• Automatic spellcheck 

• Support for Bluetooth keyboards* 

• iPod out to navigate music, podcasts and audiobooks through an iPod interface with compatible cars 

• Support for iTunes gifting of apps 

• Wireless notes syncing with IMAP-based mail accounts 

• Persistent WiFi connection to receive push notifications* 

• New setting for turning on/off cellular data only** 

• Option to display the character count while composing new SMS/MMS** 

• Visual Voicemail messages can be kept locally even if they have been deleted from the server** 

• Control to lock portrait orientation* 

• Audio playback controls for iPod and third-party audio apps* 

• New languages, dictionaries and keyboards 

• Accessibility enhancements* 

• Bluetooth improvements 

• Better data protection using the device passcode as an encryption key* (Requires full restore.) 

• Support for third-party Mobile Device Management solutions 

• Enables wireless distribution of enterprise applications 

• Exchange Server 2010 compatibility 

• Support for multiple Exchange ActiveSync accounts 

• Support for Juniper Junos Pulse and Cisco AnyConnect SSL VPN apps (available from the App Store) 

• More than 1,500 new developer APIs 

• Bug fixes

If you have jailbroken and/or unlocked your iPhone then it would be prudent to wait for iPhone Dev Team to provide an update on how the latest iPhone OS impacts a jailbroken/unlocked iPhone as you could end up bricking your iPhone.

But if you don’t care about jailbreaking or unlocking your iPhone then we recommend you to follow the following steps to install iOS 4 Software Update:

• Please check our tips (follow this link) to ensure you're ready for iOS 4 software update. 
• Assuming that your iPhone or iPod Touch is connected to your computer and you have gone through our checklist and ready for the software update, click the "Check for Update" button from the device summary page in iTunes. If your iPhone or iPod Touch is compatible with iOS 4, iTunes will tell you that an update is available for download and will guide you through the installation. 
• Please note that the entire process of downloading the update and installing it is a time consuming process, so please be patient.
• After you've successfully upgraded to iOS 4, you can checkout all the new features listed here.

As always, please don't forget to tell us how it goes.

Update 1:

It looks like the iOS 4 update is currently available only to iPhone 3G and iPhone 3GS users. It's not available to iPod Touch users currently.

Update 2:

The iOS 4 build number is 8A293. Its the same as the iOS 4 Golden Master that was released at the WWDC. So looks like as Dev Team had confirmed it will be possible to jailbreak and unlock it. However, we will wait to get a confirmation on the baseband.

Update 3:

Some of our readers are reporting that they're getting error 9006. Apple servers are probably under high load, looks like its going to be a long day.

Update 4:

The size of the iOS 4 firmware file is 378MB for iPhone 3GS. iOS 4 seems to be available for all devices. Thanks Vishnu for the tips!

Update 5: 

Some users are reporting that they are getting error -3259 network timeout. It seems to be error out while verifying with Apple. 

Update 6:

The size of the iOS 4 firmware file for iPod Touch is 315MB.

Update 7:

John, one of our readers has successfully update his iPhone 3G with iOS 4. Awesome! John, please give us your first impressions.

Update 8: 

The size of the iOS 4 firmware file for iPhone 3G is 292.1MB. mo, one of our readers has successfully updated his iPhone 3GS. 

Update 9:

Good News! The baseband is 05.13.04 so as expected, the baseband is the same as iOS 4 Golden Master, which Dev Team had confirmed can be jailbroken and unlocked. But we might have to wait as Dev Team has indicated that they will release the toold after iPhone 4 is launched.

Update 10:

iPhone Dev Team Working Hard To Release Tools To Jailbreak And Unlock iOS 4; Warn Unlockers To Avoid Upgrading To iOS 4

Update 11:

iBooks for iPhone is now available for download from the App Store. Strangely, I could find it on the App Store on the iPhone but not on iTunes. Thanks E4tH for the tip. 

Update 12:

iPhone Dev Team Release UltraSn0w 0.93 To Unlock iOS 4 Baseband 05.13.04, Also Unlocks All Basebands Since iPhone OS 3.0

Update 13:

Let's take Apple's new iOS 4 for a spin to explore the new features

First Impressions from readers:

Some first reactions about iOS 4:

mike: "ios4 looks awsome!!!!" Mike goes on to add: "after playing with ios4 for 30 mins now folders are amazing!! ios4 is really fast and responsive!! dock is awsome!! mutitasking is fast no laggs!! iphone 3GS 32gb overall nice job apple!!!!"

Vishnu says:  "when I look at the features, I was just blown away!"

Cooper: "New mail box and camera zoom are very cool."

We’ll update this post as soon as we have any more updates so stay tuned here at iPhone Hacks or follow us on Twitter.

Thanks everyone for the tip and especially Zach for the list of new features in the release notes.