From the iPhone Dev-Team:
jailbreakme.com is back!
Thanks to some serious work by @comex, you can now jailbreak your iPhone, iPod Touch, or iPad right from MobileSafari — no PC or Mac needed!
Just visit http://jailbreakme.com on your device.
For those needing a carrier unlock, use the existing ultrasn0w in Cydia on your iPhone3G or iPhone3GS. After a short testing period, we’ll push out the iPhone4 version.
Note: The earlier MMS and Facetime issues have been fixed. If you already ran the version with those problems, launch Cydia and accept its offer to update.