Sharp FO-51 Operation Manual page 61

Caller ID (Requires Subscription to Service)
Blocking voice calls
With Caller ID turned on, you can use the Anti Junk Fax function described in
Blocking Reception of Unwanted Faxes in this chapter to block voice calls as
well as faxes from your specified Anti Junk Number.
In this case, when a voice call or a fax transmission comes in from a number
you have specified as a "Junk Number", your fax will break the connection as
soon as it receives the calling phone number from the caller ID service (before
the second ring). The caller will hear a 3-second high-pitch tone to signal the
call's termination. In Australia the call will not break off until the caller has
hung up.
To use this function, enter the number that you wish to block as explained in
Blocking Reception of Unwanted Faxes (see page 61 ).
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