If it is an iPhone that someone set an iCloud account login and password for, you can’t bypass it. If it is stolen or lost, the owner may send a message to the phone which will be displayed under the login prompt. It is a wise idea and the right thing to return the phone to its owner. If it is a lost phone, the owner can track it online and know the actual location of the phone within like 20 feet but that requires an internet connection for the phone to be tracked. One of my friends was sold an iPhone but he didn’t know it was stolen with an iCloud lock on it because it was dead in battery. Upon charging it he found icloud messages saying it was stolen and to call a number. He called the number of the victim it was stolen from and he did the right thing by returning it to her because she was robbed at gun point of her iPhone in Saint Louis Park.
If you just forgot your iCloud password you can always follow the forgot password procedure or if that doesn’t work either, just take it to the Apple store and they will help you. Here is link to forgot password procedure http://support.apple.com/kb/ph2617
Even if you do a DFU or recovery mode restore it will not remove that iCloud email and password lock that the owner has setup. This feature was designed by Apple to prevent theft since iPhones are in demand. Even the New York police department told people to update to iOS 7 because of this extra iCloud security. Some previous iOS versions had ways of bypassing that gave you access to limited features on the phone but not a full bypass. I think latest iOS 7 update patched those up.
Jailbreaks like Evasion won’t help you bypass the activation or iCloud login screens either so don’t bother wasting your time with a Jailbreak app. The hackers like GeoHot and Evaders team who make iOS jailbreaks actually have great minds and the capability to help people bypass iCloud or activation locks but they only care about a jailbreak and don’t care about helping people bypass locks. It is clear that they can circumvent tough anti-exploit measures that Apple engineers set in place so they can also easily make an exploit that bypasses a simple activation lock if they wanted to.