Pass code problems

If you don't know the passcode then there is only one thing you can do. Put your iPhone in DFU mode, and restore your phone as a new device.

http://www.youtube.com/watch?v=fiTcKMZfyfk

If you have find my phone active, then you will have to first deactivate it, or the iPhone won't be able to be restored. This is new in iOS 7.

If you can't remember the code, you will have to restore by connecting to iTunes.

Well, the answers so far are incomplete. If you have synced your phone to your computer you can connect it using a USB cable, click on its name in iTunes, then click "Restore iPhone". This will back up the phone, restore iOS without the passcode and then restore the backup. You will not lose any content. If you have not synced your phone with your computer and you have iOS 7 installed you will have to remote wipe the phone. See: http://support.apple.com/kb/HT1212 for additional details.

It asks for a passcode input on the phone. It brings my only to the emergency call screen. I cannot do anything else.