well son you shouldnt have updated to 4.0 if you dont have 3.1.3 SHSH blob saved on cydia.......so here is your only solution http://forum.gsmhosting.com/vbb/f621/onesim-sim-card-offers-you-infinite-possibilities-1019726/ or if you have a mac computer you can try this http://forum.gsmhosting.com/vbb/f456/all-iphone-activate-without-any-sim-card-1039518/ and you,ll have to wait for the release of a jailbreak for 4.0