The screen-lock (device unlock) passcode for iPhone/iPod Touch isn’t the most secure method out there. The reason behind this is of course the limitation of a numeric based 4 digit code. 9 to5 Mac have realized that and have done something about it. Yup they have made it possible for you to set a 6 digit alpha numeric pass-code for unlocking your device.
This is how they did it : They created a profile out of Apple’s corporate development kit that makes the alphanumeric flavor of passcode a possibility.
Ok Ok, here is how you set the pass-code. Open http://9to5mac.com/9to5mac.mobileconfig on your iDevice. Enter a new passcode once prompted. You might want to bear in mind that while this allows for alphanumeric codes. You aren’t allowed to use consecutive digits. For e.g. you can’t have gw5678 as your pass-code, gw5791 will do the trick. In case you want to revert back to the same old pass-code scheme, then all you need to do is follow this path Settings/General/Profiles/9to5mac/ and then select the remove option.
As always, you will be doing this at your own risk and will and no one else would be held responsible for it. So do you intend to use the alphanumeric code as your screen lock pass-code.