So my iphone 4 is still on 4.0.1. I want to upgrade to 4.1 for my apps to work and hopefully the proximity sensor, but 4.1 can't be jailbroken or unlocked. And Apple is no longer signing 4.0.1 for downgrading, I'd like to know how to save the hash or shsh something? I've heard I can jailbreak my iPhone and save the hashes so I can restore to 4.0.1 at a later date. Still true? If so how would I go about doing that? Just backup, jaibreak, save hash (how to), restore and upgrade to 4.1 then restore from backup? Thanks!