If you have the unlocked iPhone 4 on baseband 01.59.00 and you want to update to iOS 4.2.1 chances are you will likely be updating to 03.10.01 and therefore losing your carrier unlock. Updating to iOS 4.2.1 using TinyUmbrella will protect your baseband update allowing you to carrier unlock your iPhone 4 again. You can follow the tutorial below on how to upgrade your iPhone 4 to iOS 4.2.1 preserving its baseband using TinyUmbrella. Note: Before you continue, you must have Saurik’s server in yoru host file. At the end of the file add the string 74.208.10.249 gs.apple.com which is useful to redirect requests for certificates for authenticity that iTunes will make to the Saurik server. If you don’t know how to do that, follow the steps below: Mac users Navigate to Go -> Go to Folder and enter the path /etc Open the file hosts with TextEdit, add the following string 74.208.10.249 gs.apple.comand save the file to your desktop. Now return to the previous folder by following the same method and copy the text within this file by replacing the original file (If prompted for a password enter it and click OK) Windows users Open Notepad with administrator privileges and then right click on the icon of notepad and click on “Open as administrator” Now that Notepad is open Go to folder C:/WINDOWS/system32/drivers/etc and open the file Add the following line at the end of the document and save it: 74.208.10.249 gs.apple.com Step 1: Update iTunes to iTunes 10.1.2 by going here. Step 2: Download TinyUmbrella by clicking here. Step 3: Connect your iPhone to your Mac. Step 4: Right Click the TinyUmbrella and select “Run as administrator” to open it. (If you get a Windows Security Alert, make sure both boxes are checked, and hit Allow Access) Step 5: Make sure that your device is connected correctly, so that TinyUmbrella can detect the type of device and its firmware. Step 6: Make sure Cydia or TinyUmbrella has an SHSH of the latest firmware. You can do this by simply clicking “Save my SHSH”. (At this point TinyUmbrella attempts to check for your SHSH blobs on Saurik’s server as well as save your current ones locally) Step 7: Now minimize TinyUmbrella (we will not be using TinyUmbrella’s TSS Server for this as it won’t allow localhost resolution) Step 8: Open iTunes and backup you iPhone (anytime you do an update or jailbreak you must backup your phone) Step 9: iTunes will offer you the update to 4.2.1 click Download and Update. Step 10: Once your installation has started it will take a couple of minutes to actually complete Step 11: After your phone reboots for the final time iTunes will error out with a 1013 error. This is what we were looking for. Notably, the baseband has not updated. Step 12: Close all of iTunes error pages and iTunes itself Step 13: Go back to TinyUmbrella and click Exit Recovery. Your phone should be rebooting and will come up to the home screen Step 14: Go to Settings>General>About verify that you are still on the same baseband as before. Step 15: Jailbreak your iPhone 4 iOS 4.2.1 on baseband 01.59.00 using our Greenpois0n RC5 iPhone 4 / iPhone 3GS guide here. Step 16: Carrier unlock your iPhone iOS 4.2.1 using our Ultrasn0w guide here. As usual, stay tuned for more guides and how-to’s regarding your iOS devices by following us on Twitter and/or subscribing to our RSS feed. Authors:

to know more click here