Step 1: preparations
This iPhone Jailbreak guide requires you to download the following:(1) RedSn0w for Windows, Mac or Linux; (2) the official Apple iPhone restore file (.ipsw) for iPhone 3G.

Step 2: Upgrade iTunes to the latest version and check iPhone IOS updates.
upgrade your iTunes to the latest version (currently 9.2.1) and backup your iPhone. Then check if your iPhone is running the right IOS.

Step 3: Run RedSn0w
Launch RedSn0w and click “Browse.”
Select the IOS 4 .ispw file and click next.
Turn off your iPhone and make sure it’s plugged in read the instructions on the screen.
Click next and follow the onscreen instructions.
Hold the power button in for the allotted amount of time.
Then hold both the power and the home-screen button in together.
Finally, just hold the home-screen button.
In under a minute, you will have a Jailbroken iPhone 3G.

That’s it, you’ll see the following two screens while Cydia, the jailbreak app store app, is installed and then you’re ready to go. Cydia is part of the RedSn0w package and will install as a app on the iphone, you will then be able to install jailbreak apps using Cydia.

Let your iPhone reboot, open Cydia and download a bunch of cool apps and modifications that you could not otherwise download with a factory iPhone.

In the App Store NOW:
• Dropbox – Sync your Dropbox files in the background.
• Evernote – Download and upload notes in the background, and continue recording voice notes while you’re messing around in other apps.
• Zagat
• LinkedIN
• How To Cook Everything
• Trapster – Background locations
• Bejeweled 2
• DocsAnywhere
• Motion X GPS – Record tracks in the background; hear background voice coaching.
• TuneIn Radio
• OffMaps
• WeightBot
• WordPress – Fast app switching, Retina Display optimized
• TomTom – Background navigation directions
• DiveLog
• textPlus
• Plants vs Zombies – Fast app switching
• Radio Box
• NYTimes
• Last.FM
• Tripit
• ESPN ScoreCenter
• Colloquy – Multitask ready and optimized for the Retina Display.
• FlightTrack Pro – In-app SMS flight sharing
• Pandora – Play your Pandora music, WHILE DOING OTHER STUFF! Essential.
• Pastebot
• ooTunes Radio
• RunKeeper
• Promodoro
• Tap Tap Revenge 3
• Twitter for iPhone
• Rooms for IRC
• Ustream Viewing Application
• TomTom US & Canada

Hitting the App Store with iOS4 updates soon:
• Navigon – Navigon will keep shouting directions at you while you’re working in other apps.
• Skype – Will soon let you multitask while talking to grandma.
• MyPhoneDesktop
• Nap App
• Occasions – Local notifications
• MotionMeter
• Batting Goggles
• Amp Music Player
• Slacker Radio – Slacker Radio recently got caching, and soon it’ll get multitasking support as well.
• PlaceTagger
• Rockola.FM
• Task Aware

The update currently works for the iPhone 3G and 3GS as well as second- and third-generation iPod touch players. iPads get the update later this year. Both the original iPhone and first-generation iPod touch are ruled out as their hardware isn’t capable of handling the update. Patching requires iTunes 9.2 and checking for an update in the device’s general setup pane.

AT&T didn’t provide US-specific tallies but claimed that iPhone 4 pre-orders were about 10 times higher than it saw with iPhone 3GS pre-orders last year. It explained that its suspension of pre-orders was to simply make sure the company could fulfill the orders it already had. Pre-orders might restart if Apple can supply more stock, the carrier said.

The company also justified the repeated system failures, noting that there were over 13 million visits to AT&T’s eligibility page, or three times more than its previous record.

Both records promise an extremely high sell-through rate of the iPhone 4 and could easily smash last year’s launch weekend sales record, where one million iPhone 3GS models were sold in three days. Analysts have already been raising sales expectations for the June 24 intro and have suspected that Apple could sell two million phones by the following Monday.