Polycom VVX 300 Owner's Manual page 18

b If you selected No Answer, you will see that your phone number is
entered in the Contact field by default. By entering your own phone
number in this field, the phone will send callers to your voicemail box if
you do not answer. You may enter a number to forward all
unanswered incoming calls to and how many rings to wait be-
fore forwarding (one ring is approximately 4.5 seconds). A value of 5
is recommended.
c If you selected Busy, you will see that your phone number is
entered in the Contact field by default. By entering your own phone
number in this field, the phone will send callers to your voicemail box if
your phone is busy. You may enter a number to forward all future
incoming calls to when all of your incoming lines are busy.
4. Press the Enable key to confirm call forwarding.
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