Also known as selective call block and selective call rejection. 1. A CLASS service feature of the public switched telephone network (PSTN). Selective call rejection screens incoming calls against a userdefined list of acceptable telephone numbers. Calls from those numbers are diverted to a recorded message. Calls from all other numbers ring through as usual. See also CLASS and PSTN. 2. As defined in the advanced intelligent network (AIN) specifications, call block can work on incoming or outgoing basis. On an incoming basis, the feature allows the subscriber to program some number of telephone numbers from which incoming calls are denied. Incoming call blocking is widely available. On an outgoing basis, this feature typically supports the blocking of calls to international destinations, either in total or to specific country codes. Content blocking supports the blocking of calls to specific numbers, such as 900/976 numbers. This capability is deployed fairly commonly in many foreign networks, but is not widely available in the United States. See also AIN and selective call rejection.