Cisco IP phone hard reset

Cisco IP phone hard reset.
Model: 7911/7912
  1. hold # key and wait several sec until the red indicator light up
  2. press the key sequentially -> 123456789*0#
Model: 7971
  1. hold # key and wait several sec until the red indicator light up
  2. press the key sequentially ->  3491672850*#
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