Note: If you have iPhone 3GS you will be asked at some point (after step 4 maybe) what bootroom you have. If you choose to detect it for you, you will have to put your device in DFU mode and follow on-screen steps
You can later install 06.15.00 iPad baseband.
Step 1: Download the iOS version for your device using our iOS Versions Tools
Step 2: Download redsn0w sn0wbreeze 2.5 using our Jailbreak Programs Tool
Step 3: Connect your device to pc. Open sn0wbreeze 2.2 as administrator if you are using windows
Step 4: Choose the iOS you downloaded at step 1 and if sn0wbreeze says it`s ok, press the blue button to continue
Step 5: Sn0wbreeze has 2 options: simple and expert. Simple it`s…well, the most simple method and expert will let you customize your firmware. Both versions preserve baseband. There is also an option called “baseband preservation mode”. You will not jailbreak or unlock your device, but simplu upgrade your iOS version to 4.2.1 without baseband update.
Step 6: Main menu, General Option – will go through all options. Select it and press the blue button
Step 7: Choose desired options
Step 8: Return to main menu and press build ipsw. No wait. You can play PacMan meanwhile :)
Step 9: Push the ok button and put your phone into DFU mde
Step 10: Open iTunes and press shift+restore. Load the custom ispw file.
You have a jailbroken device now.