Panasonic KX-TGM420 Operating Instructions Manual page 85

Blocking unwanted callers:
When a call is received, the unit rings once*1 while
caller information is being received.
If the caller's phone number matches an entry in the
call block list, the unit emits no sound to the caller,
and disconnects the call.
*1 If you do not want this one ring to sound, select
"No" in "Turning the first ring on and off" (page
88).
Storing a single phone number
Important:
• We recommend storing 10 digits (including the area
code). If only 7 digits are stored, all numbers that
have the same last 7 digits will be blocked.
Adding call blocked numbers from the caller list

1 [ ] CID
2 [ ]: Select the desired entry to be blocked. 
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