how do i unlock iphone forgot password

If you cannot remember the passcode, you will need to Restore your device...

Connect to iTunes on the computer you usually Sync with and Restore...

http://support.apple.com/kb/HT1414

If necessary Place the Device into Recovery mode...

http://support.apple.com/kb/HT1808

You have to restore the iPhone via iTunes...start iTunes, connect the USB end of the cable, then while holding the home button on the iPhone connect the dock-connector end of the cable. That will put you in recovery mode and you can proceed to restore the iPhone from backup.