Yealink SIP-T48G - Manual (Page 119)

Basic Call Features
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The touch screen prompts “Copy to all lines?”.
2) Tap the OK soft key to accept the change or the Cancel soft key to cancel.
c.) If you select No Answer Forward:
1) Tap the On radio box of the No Answer Forward field.
2) Enter the destination number you want to forward unanswered incoming
calls to in the Forward To field.
3) Tap the gray box of the After Ring Time field.
4) Tap the desired ring time to wait before forwarding from the pull-down list.
The default ring time is 12 seconds.
5) (Optional.) Enter the no answer forward on code or off code respectively in
the On Code or Off Code field.
You can also enable no answer forward for all accounts. Do the following:
1) Tap the All Lines soft key.