[Asterisk-Users] Is an unregistered phone busy?

[Rob Scott]

Asterisk seems to regard an unregistered phone to be busy.
Is that correct? Is not an unregistered phone unavailable?

It is odd to me that if someone dials an unregistered extension, then
the dialplan jumps to busy and voicemail kicks in saying that the person
is on the phone, when clearly they can't be if the phone hasn't
registered.

Any way around this?