Remeber that if you disconnect the cable from the processor, the voicemail system won't work correctly, so reconnect after you are done testing. I would plug into the Netgear data switch thst you described, and unplug the cable to the wall. This would remove the connection to the rest of the network.
Ping test is the same as to computers, from command prompt PING {IP ADDRESS}
The community name and how to enter programing on the phone won't be discused in the open forum.
Settings should not be lost. They are stored by battery and also on a SD media card, as long as the last person that made changes backup up to that card. Voicemail is storerd on a hard drive or flash drive depending on the system.
The PBX should be up and going in about a minute. The voicemail may take longer, 10-15 minutes if it is a Stratagy IES like I believe it to be. After the voicemail has been shut down, just rock the power switch off, then back on.
