While Sn0wbreeze 2.7.1 can already jailbreak iOS 4.2.8 on Verizon iPhone 4, the problem is that it is for Windows users only. If you happen to be a Mac user, and want to untether jailbreak your Verizon iPhone 4 on iOS 4.2.8, you can do so now with this PwnageTool bundle.
iOS 4.2.8 is also available now for CDMA iPhone 4 users on Verizon, alongside iOS 4.3.3 for GSM iPhone 4, iPad 2, iPad, iPod touch 3G/4G to fix the much talked about iOS location tracking bug.