The default code for the phone to access this menu is the last 4 of the phone number. If the code was changed, you can dial *228 and choose option 1 and the code will reset to the last 4 of the phone number
There is not a code to discover the numbers that other people are restricting. As Supergirl stated, you can restrict your own number by dialing *67 before making a call. You can unrestrict your own number by dialing *82 before making a call. I'm not sure what elrey was referring to, I think he thought you had a lock on your phone preventing you from accessing the menus. But unfortunately, there is no way to find out who is calling you from a restricted number. If you know who's calling you and their number, you can block their number with a free service called call & message blocking, and even though they are blocking their number, the switch will recognize the number its coming in from and won't allow it to go through to your phone. If you do not know the number, you can block all restricted or private callers through usage controls.