Verizon iPhone 4 can now be jail broken on 4.2.8 using Pwnagetool for Mac. This tool is specifically for mac and is made by the iPhone Dev team. I will post a guide for the latest AT&T iPhone 4 jailbreak as well.
Here is the original post and downloads:
Verison Mac: http://bit.ly/lzMJL2
Guide for 4.3.3 AT&T: http://bit.ly/kde0qN
Snowbreeze for Windows & IOS 4.3.3: http://bit.ly/if4I6S
Redsnow for Mac & IOS 4.3.3: http://bit.ly/lwh6LM