Originally Posted by Big Calhoun
Unknown usually occurs in the case of trunks and WATS lines. Again, with trunks, the caller ID information is passed from the phone originating the call. So if that phone doesn't transmit that information, the Central Office really doesn't know which actual line originated the call. Most trunk lines are assigned 'fictitious' numbers which can't be dialed directly. WATS line are essentially the same, it's just a batch of numbers. However, WATS lines are strictly for outgoing calls (think of a call center).
Blocked means someone is purposely blocking their number. So the Central Office knows the line that originated the call, but the customer has activated a feature to prevent the information from being passed.
They are two different conditions and are treated differently in call processing. Now don't forget, you can get a Caller ID spoofing card. It works like those pre-paid phone cards. Basically you call a number, say what number you want passed through caller id, and then dial the actual number you want called. Telephony is a very interesting world.
