I have a 3gs with 3.1.2 OS, 05.11.07, jailbroken with Spirit and unlocked. ECID SHSH saved through Cydia. Now I'd like to update it to iOS 4.x and, of course, keep it jailbroken and unlocked.
All tutorials I've seen assume non-Spirit jailbroken units but say nothing about how to go to iOS from Spirit. Some time ago I tried some un-Spiriting suggestions (forget what now) and upgrade to 3.1.3 but I kept getting the 1600 error. After that I gave up---until now.
Does anyone have any good suggestions how to proceed in this case? I wouldn't care much about iOS upgrade but some apps I really want require it.