If we upgrade a carrier unlocked iPhone 3G or 3G S to iOS 4.2.1 firmware or any other version it will lose its activation and become unusable. Those people who bought unlocked iPhone models will get into trouble if they upgrade to new iOS without checking for the availability of compatible jailbreak/unlock tools. The iPhone will then keep itself locked at the “No SIM card inserted” message and with a connect to iTunes screen. And another message ” The SIM card inserted in this iPhone doesn’t appear to be supported” when we connect the device to iTunes. That means you have to get the original carrier SIM card to activate the iPhone 3G or 3G S again. But you can override this using activation of hactivation tools designed for the specific iOS version. Thanks to the iPhone-dev team and other iOS hackers around the world. Now we can fix SIM not supported message in iPhone 3G and 3GS after iOS 4.2.1 firmware upgrade too.
Activate iPhone 3G or 3GS without original SIM card after iOS 4.2.1 upgrade:
First you need to jailbreak your iPhone 3G or 3G S with iOS 4.2.1.
Download iOS 4.2.1 here.
Download Redsn0w 0.9.6b6.
Now run Redsn0w 0.9.6b6 and point it to the iOS 4.2.1 firmware ipsw. Redsn0w 0.9.6b6 will then process it will take you to the next step. Select to install iPad baseband, Cydia and follow the steps shown in Redsn0w 0.9.6b6 interface to enter into the DFU mode. Wait for the Redsn0w 0.9.6b6 to complete jailbreak process and reebot the phone. Note that the Redsn0w 0.9.6b6 jailbreak is a tethered jailbreak for iPhone 4 and new iPhone 3G S model. The iPhone 3G and iPhone 3G S ( old bootrom) users can use the following method to activate their phone and fix the SIM not supported message.
Open Cydia, go to manage and then sources.
Now click on edit and add a new source URL http://repo.bingner.com.
Go back to manage and search for Binger and then SAM and SAMPref from sources, and install them.
Run Redsn0w 0.9.6b6 again and in the second step, select deactivate and continue. Now reboot the phone, connect to iTunes and activate. That’s it you have activated your iPhone 3G/3G S on iOS 4.2.1 firmware just like the official method.