I am in desperate need of help. I need to upgrade from 3.1.3 to anything 4.0 or higher but I need to keep my unlock and jailbreak because I have tmobile. Can someone help?
Create a custom 4.3.3 firmware (with options to keep the current baseband and activate if you don't have the official carrier sim) yourself using Pwnagetool(Mac) or Snowbreeze (windows). Or, you can google and download one from a trusted site.
Once you have the custom file, use Pwnagetool(Mac) or Rednsow (windows) to put the phone into a special DFU mode, and then, restore with the custom firmware file through iTunes. Afterward, on the phone, install Ultrasnow if you need the phone unlock to use on non official carrier.