Most people use the Set Install or Replacement PIN...
Connect the phone to the network and allow it to connect to the 3300... if the MAC address isn't recognized, it will show ask for the PIN... like "ENTER PIN AND PRESS HOLD" or something similar (exact verbiage/key depends on set type), and enter the Install PIN (*** in most default installations, but you could check your system options form) and the extension.
So if the new extension is x1234, when the phone comes to the PIN screen enter ***1234(HOLD) and the MAC address of that device will be associated with that user in the system and the phone will come online... If it is replacing an existing user, the Set Replacement PIN (### in many installations) can be used instead, say if the phone on x1222 went bad and needed to be replaced, disconnect it and install the new set, and when it gets to the PIN screen, enter ###1222(HOLD) and the MAC on that user will be swapped with the new set. Note this only works if the set type (5330, 5360, 6930, etc) are correct and match to the set.
