my 3gs 3.1.3 with official carrier, was JB using spirit, SHSH was saved to cydia. Downgraded it to 3.1.2 using cydia host entry - got error at the end, but that's ok, used blackra1n to JB in 3.1.2, then used sn0wbreeze to cook a custom ipsw without hacktivation, restore in itunes and all is working great (besides the ios4 issues )