Before you pack up the 212, be sure to delete it off of your OBiTALK dashboard and wait a few minutes while it is remotely reset. Then, unplug the Ethernet cable, leaving the power cord plugged in, pick up the phone, and key in ***8 then 1# to restore it to factory defaults. Then you can power it off and pack it up.
This is just in case the seller resells it to somebody else, instead of returning it to Poly.