iPhone 4 was recently jailbroken and now it is unlocked too, thanks to the Dev Team. It cannot be easier, no PC/Mac required, only the internets!
All you need are the following :

A Jailbroken iPhone 4 / 3GS,3G (it should be activated, that is a pre-req for online jailbreak)
A WiFi connection
That is pretty much it!

Step by step (best practices) :

Launch Cydia and search for ultrasn0w [if not found, then add repo : repo666.ultrasn0w.com in Cydia]
Install ultrasn0w and reboot your iPhone 4 when prompted. Turn 3G off  (Settings -> Network -> Enable …

CAUTION : iOS 4 jailbreak is way complicated unlike other jailbreaks. Please proceed with caution.
Requirements :

Jailbroken iPhone 3GS with older bootrom.
You haven’t used Spirit jailbreak before (for untethered jailbreak).
You have Windows (PC). For Mac, try Pwnage instead.
Please read the above requirements again.

More info about these custom firmware files :

[UPDATE] : You need to download files from either step 1a or 1b depending on your baseband preference. Both are unlockable, so I would go with step 1b which is the latest baseband which supposedly does better with the battery. step 1b …

iPhone 4 is awesome with stunning hardware, looks making all other iPhones feel dumb and stupid! Apple cleverly left out ‘G’ from ‘iPhone 4G’ hinting at an impending iPhone 4G rollout expected in 2011. iOS name is licensed from Cisco to differentiate iPhone OS 4.0 from iPhone 4 I believe. There are some things we should be aware of before starting to obsess about the iGadget of the year!

AT&T’s Dirty Tricks yet again

AT&T is doing everything possible to tap the existing users into 2 more years of iPhone contract by …