POE provides your customer peace of mind in the event of an power failure and will prevent phones from rebooting when there are spikes or brief outages. A mid-span solution like Red-Hawk Powersense will work with existing switches and a POE device port basically gets inserted between the switch and the punchblock of any line that will support a IP phone. POE will only send power when device on other end supports it or behaves like a normal " power-less" Ethernet port.