Apple released iOS 4.2 for the masses finally. While it does some nice things on an iPad, there isn’t much for iPhone 3G/3GS/4 if you are happy with the current jailbreak+unlock.
You are urged to download TinyUmbrella and save your current firmware SHSH files. It is available on multiple platforms (Linux, Mac, Windows). The SHSH window for signing your firmware version is almost closed, so better hurry.
Cydia for 4.2 firmware doesn’t even work the traditional way, nor is there an unlock available as of this writing. So, kindly ignore the iOS 4.2 update on iTunes and wait for further tools/hacks to continue the jailbreak+unlock fun!