Calling-party privacy requested by any intervening system or network may prevent the caller from being called. Because of services enroute, the calling-party number may be anonymous. Therefore, the number is not callable.

The caller may have routed through the originating network with an abbreviated caller ID, and then transited to the local system without having the number made fully qualified. Because of this, the calling number received may be formatted invalidly; and therefore, unreachable.

The caller may have a number that cannot be dialed directly. Because of this, the calling number received may be unreachable.