Call blocking is implemented to prevent the unauthorized use of phones. Call blocking matches dialed numbers against a pattern of specified digits, and matches the time against the time of day and day of week or date specified. Up to 32 patterns of digits can be specified for call blocking. Call blocking is supported on IP phones only, and not on analog Foreign eXchange Station (FXS) phones.
When a user attempts to place a call to digits that match a pattern that is specified for call blocking during a time period that is defined for call blocking, a fast busy signal is played for approximately ten seconds. The call is then terminated, and the line is placed back in on-hook status.
Call blocking applies to all IP phones in a Cisco Unified CallManager Express system, although individual IP phones can be exempted from all call blocking.
If there is an after-hours call block configured 7-24 to prevent calls to certain locations when the Cisco CallManager Express/Cisco Unified Survivable Remote Site Telephony (SRST) gateway is configured, the CallManager SRST phones can register in fallback mode and cause calls to fail. This can happen even when not in SRST mode. After-hours call blocking takes effect for all Plain Old Telephone Service (POTS) and VoIP dial-peers in Cisco CallManager Express 4.0. This way, if H.323 dial-peers fallback to Cisco CallManager during normal operation, the CallManager phones can be subject to after-hours settings on CallManager Express.
In order to prevent this behavior, configure the paramspace callsetup after-hours-exempt TRUE command under the dial-peer routing calls to the Cisco CallManager.
The phones are still subject to the after-hours block after they are in Cisco CallManager Express fallback mode.