Most phones with a contact list or native phone book allow the user to block specific numbers or contacts either from the phone settings or directly from the contact list. In some phones, it may be necessary to use a third-party service or to download an application.
For phones with a native phone book, the blocking feature is found under "Settings," then "Phone" and then "Calls" or "Incoming Calls." Depending on the phone, there should then be an option for "Block," "Blocked Callers," "Unwanted Calls," "Blacklist" or something similar.
After selecting the appropriate menu option the contact list or phone book generates. By selecting the phone number or contact to block and confirming the action, the caller will no longer ring through or appear on the cell phone monitor when calling the cell phone number. The caller will either hear a message that the phone doesn't accept calls from his number or a busy signal.
Android phones have a similar process for blocking calls. From the "Contacts" option, the user may choose the person or number he is trying to block. From there he selects "Menu," then "Options." There is a checkbox option entitled "Incoming Calls - Send calls directly to voicemail." Once confirmed, blocked callers go directly to the recorded voicemail greeting, bypassing ringing through on the phone.