Just a word of advice for those on Softbank with 3GS. If your wifi disappears after you JB and install an app and you do the usual fix:
1. Turn your phone to airplane mode
2. General>Reset>Reset Network Settings
MAKE SURE YOU DISABLE 3G BEFORE YOU RESET! I've just had to restore twice to figure it out, if you don't, the phone hangs on the Apple Logo and I couldn't reboot it by any other method other than doing a full restore. Don't know if it's ONLY applicable to Softbank but I did the same thing in another country last week without switching 3G off and it didn't lock up at all.
1. Turn your phone to airplane mode
2. General>Reset>Reset Network Settings
MAKE SURE YOU DISABLE 3G BEFORE YOU RESET! I've just had to restore twice to figure it out, if you don't, the phone hangs on the Apple Logo and I couldn't reboot it by any other method other than doing a full restore. Don't know if it's ONLY applicable to Softbank but I did the same thing in another country last week without switching 3G off and it didn't lock up at all.