I recently purchased an ESI Bluetooth Headset Interface for testing and just goofing around with. Documentation says it will work with "ESI 48-Key Feature Phone (Digital or IP Feature Phone II)" but that does not appear to be the case. I did manage to get it to work on a digital phone but when I tried to plug it up to an IP Feature Phone 2 I get nothing on the Bluetooth interface, it is just dead.
We do not currently have PoE switches so are using various injectors around the office the one I have been testing on is a TrendNET TPE-105I.