Plugin the phone, wait until it says 'x' seconds until boot. Hold the 8,6, and * keys down until a password prompt appears (This is not the same as the 'setup' option at boot). Then enter the mac address of the phone (if you need the address, boot the phone normally and pick 1, 2, 2) in all lowercase with no ':'s.
This should reset the password to 456 and you can reconfigure, It should still have all the other configuration intact.