Not illegal, apart from probably voiding the warranty and EULA, but meh, my understanding is it just allows you to install software directly on to the Apple operating system and bypass other features so you don't need to be online to get these things.
Jailbreaking is not illegal as was ruled by the courts, it does void your warrenty however you can un jailbreak thus they would never know actually as long as they did not install an custom firmware or change the baseband. Jailbreaking allows you to install apps that are not on the apple app store thus apps that apple did not approve can be installed, it also allows multiple customizations to be done by allow a little bit more freedom to the operating system, you can change themes, lock screen, how your phone looks and other things a long that line.
<3 "I'll never let you fall, I'll stand up with you forever. i'll be there through it all" <3
Last edited by Sistrurus; May 23rd 2012 at 04:30 PM.