Let me share you my experience. I woke up this morning to find my wifi capabilities on my iPhone to be grayed out,which looks like this:
This was after the unlock process I went thru using blacksn0w on Cydia,I am by the way on an iPhone 3GS too running on 3.1.2 JB'd.I ran all the basic t/s steps I could think of like turning the phone on and off,resetting network settings and etc.And it seems that the t/s that did the trick was a soft reset.I got my wifi to work again.But it kind of freaked me out and at the same time it got me paranoid that it might do it again...