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 dialing 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 dialing "611" from your landline telephone or calling your local telephone company's business office number) to subscribe to this service.
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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.