I've been out of the jailbreaking scene for a while; my iPod Touch 2G hasn't been touched at 3.1.2 and my iPhone 4 is currently unjailbreakable. Recently my dad bought a 3GS (8GB, iOS4). I'm assuming it's got the new bootrom, and after reading some more it seems that could be a problem. I'm hoping to unlock it so that he can use it with China Mobile. Is it possible to downgrade it to 3.1.3, then jailbreak it with Spirit and ultrasn0w? Also, I've heard some downsides of using Spirit.. anyone care to list them? It's been so long since I've done any work with my iDevices and I have almost no clue what SHSH blobs are (besides the fact that they're important for jailbreaking and downgrading).