iPhone

How difficult is it to unlock iPhone? The start up screen says it all (Slide to Unlock, LOL).

Seriously though, when you need to utilize a buffer overflow exploit and SSH to replace system files on a cellphone, it's definitely not for the faint hearted. Here is a comprehensive guide on jailbreaking and unlocking iPhone with firmware 1.1.1 on Windows. A word of caution: the guide may not be completely up to date and, needless to say, you're risking voiding your warranty and bricking your iPhone.

it's comforting to know that in most cases, you can set iPhone to recovery mode and restore the default settings (Turn off, hold Home key and plug the USB connector. iTune will deal with the rest).