Anonymous calls, which sometime show up as "Unknown" or "Unavailable" on caller ID, can be a nuisance to landline telephone users. While some calls marked as "Unavailable" are legitimate communication and cannot be blocked, a majority of these calls can be diverted by simply dialling a code from a properly equipped landline telephone.
Subscribe to Anonymous Call Rejection. This service is free for many telephone users and may already exist on some home telephone lines. If the service is not already on your telephone line, or if the steps here do not work for you, contact your local telephone company (either by dialling "611" from your landline telephone or calling your local telephone company's business office number) to subscribe to this service.
Pick up your telephone receiver. Using any wired or wireless landline telephone, pick up the receiver and listen for a dial tone.
Press "*77" to activate the Anonymous Call Rejection service from your touchtone landline telephone. If you use a rotary dial telephone, the rotary equivalent code to dial is "1177."
Listen for a confirmation. Depending on the equipment your telephone company uses, you may hear either a quick "buzz buzz" sound or a recording informing you that you have successfully activated the Anonymous Call Rejection service. You should not hear a busy signal, a fast busy signal, or a recording indicating that your call cannot be completed; if you hear any of these messages, you may not be subscribed to the Anonymous Call Rejection service.
The Anonymous Call Rejection service is free for many customers, but it may incur a nominal monthly (or per use) charge in some local markets. The Anonymous Call Rejection service intercepts and blocks callers who have intentionally blocked delivery of their telephone number; legitimate callers with no caller identification information--such as police departments, battered women's shelters and government offices--cannot be blocked. If you wish to turn off the Anonymous Call Rejection service, simply dial "*87" (or "1187" for rotary dial users) from your landline telephone.
Using the Anonymous Call Rejection service will not affect how your own caller identification is displayed to called parties. Although blocking "Unavailable" numbers may stop some callers, all threatening or harassing telephone calls should be reported to local law enforcement officers to ensure personal safety.