Hello,
Several times a month our recepitionist's phone will have the display go black and not ring or respond until rebooted. We have tried swapping the vvx500 with another vvx500 and a vvx600, as well as changing the port on the poe switch that it plugs into. None of the other 20 or so extensions have this happen. She is the first in a call queue, so we mostly find out when the next person in the queue tries to transfer a call to that extension and it rings their own phone. What could some possible causes of this be?