Dev team has launched redsn0w 0.9.7 beta 4 with usbmuxd lets you jailbreak iOS four.2.1 (untethered). The replace will will let you jailbreak into all of your iOS four.2.1 gadgets and that embody the iPhone four, iPad and iPod Contact.
The official change log is as follows:
Starting with this version, redsn0w no longer requires you to install and run a separate program for the usbmux (this was a non-trivial procedure for many). It’s okay to keep that program running if you normally use it for ssh anyway. We also think we’ve fixed a race condition in the GUI that was causing redsn0w to crash during the “Preparing JB Monte Files” step. Nothing at all has changed on the iPhone side (where the main issues are still just Bluetooth and Skype).
Also, if this statement from the official Redsn0w testers account is anything to go by, the Windows version of Redsn0w 0.9.7 will follow soon after this fourth beta release for OS X:
Today’s beta4 will eliminate separate usbmuxd process (so many more Mac users can use it). After that, expand to Windows.
NOTE:: All the standard warnings mentioned previously still applies. RedSn0w 0.9.7 beta 4 is available by following the link below and our complete step by step guide posted here to jailbreak (untethered) iPhone 4, iPad and iPod touch 4G on iOS 4.2.1 with Redsn0w 0.9.7(obviously you will have to skip the step of USBMUX). Remember this is still a beta.