I've got a bunch of Poly VVX-250 VOIP phones that work fine as kind as long as they are plugged into the wall wart. Recently I got around to install a couple of TP-Link 5 port POE switches that are added to the existing plain Jane 24 port unmanaged switch. Great!!! Finally I am able to ditch the wall warts from these phones making more space on the desk, plus I am gaining some badly needed power outlets. So I thought. 
Plugged in the first VVX-250 into the POE switch, booted up no problem. Plugged in the other Poly phones and they start to boot anywhere from 5 to 15 seconds, then they play dead.
Not even a back light on the display. 
Cruising around the interweb I found tons of people having the exact same problem only repairable by purchasing new phones.
Here are some good news fellas!!! I was able to fix all my bad VVX-250 VOIP phones that only worked with the wall wart this way:
I used a TP-Link TL-SG1005P Version 5 POE switch (5 port). On the back of the unit are 2 switches. One for Auto Recovery and one for Extend. The Extend switch only works on port 1 and 2 of this switch, keep this in mind.
Step 1: Plug the POE switch in and turn the Extend switch on the back of the unit to the ON position. I left the Auto Recovery in the OFF position.
Step 2: Plug in port 5 of this POE switch via a short CAT 5E or Cat 6 cable to your router or other non POE network switch, any free port is good.
Step 3: Plug in your Poly VVX-250 into Port 1 of the POE switch. You notice a green LED on the right and an orange blinking data LED on the left. VOILA and your VVX-250 boots like normal. Let it finish booting and logging in.
Step 4: Unplug your VVX-250 from the POE switch port 1 and immediately plug it into port 3 or port 4 (remember these don't have the POE extend function) and let it boot fully up. Make a phone call id you want.
Step 5: Turn the Extend switch to the OFF position on the back side of TP-Link switch (so you get Port 1 and 2 back into normal POE).
Step 6: You notice that on the port you got the VOIP phone hooked up to now both LED's on the POE switch are Green and the phone works normal.
Step 6: ENJOY!
I am not sure why the short period of extra POE voltage fixes this issue on these VVX-250 phones, but after this treatment all works like it supposed to.
All my POE phones that had trouble not working on POE (actually most of them didn't) work now fine as kind.
Hopefully this helps!
Plugged in the first VVX-250 into the POE switch, booted up no problem. Plugged in the other Poly phones and they start to boot anywhere from 5 to 15 seconds, then they play dead.
Not even a back light on the display. Cruising around the interweb I found tons of people having the exact same problem only repairable by purchasing new phones.
Here are some good news fellas!!! I was able to fix all my bad VVX-250 VOIP phones that only worked with the wall wart this way:
I used a TP-Link TL-SG1005P Version 5 POE switch (5 port). On the back of the unit are 2 switches. One for Auto Recovery and one for Extend. The Extend switch only works on port 1 and 2 of this switch, keep this in mind.
Step 1: Plug the POE switch in and turn the Extend switch on the back of the unit to the ON position. I left the Auto Recovery in the OFF position.
Step 2: Plug in port 5 of this POE switch via a short CAT 5E or Cat 6 cable to your router or other non POE network switch, any free port is good.
Step 3: Plug in your Poly VVX-250 into Port 1 of the POE switch. You notice a green LED on the right and an orange blinking data LED on the left. VOILA and your VVX-250 boots like normal. Let it finish booting and logging in.
Step 4: Unplug your VVX-250 from the POE switch port 1 and immediately plug it into port 3 or port 4 (remember these don't have the POE extend function) and let it boot fully up. Make a phone call id you want.
Step 5: Turn the Extend switch to the OFF position on the back side of TP-Link switch (so you get Port 1 and 2 back into normal POE).
Step 6: You notice that on the port you got the VOIP phone hooked up to now both LED's on the POE switch are Green and the phone works normal.
Step 6: ENJOY!
I am not sure why the short period of extra POE voltage fixes this issue on these VVX-250 phones, but after this treatment all works like it supposed to.
All my POE phones that had trouble not working on POE (actually most of them didn't) work now fine as kind.
Hopefully this helps!