There was a solution built for thin/thick clients internally to one-two buildings. They use a script to collect all the arp (MAC)information from the switches and dump that into a file (CSV) which gets put into a MySQL database (MACDB). A vbscript on the desktop (thin/think) gets the user logon ID and MAC address of the client pushes a (login/logout) to a PHP server which then looks at the phone MAC address associate with the client machine and then performs a login or logout of the device. There are logging features and Exclude phone or user tables if people do not roam or permenant locations that the logout profile gets populated with their corresponding information. From what I gather Cisco was very interested in how it worked. Its great for small or midsized companies, possibly large but depends on how many switches you have to poll and how often. I thought a simpler solution would be to have the client present you an option for EM and you just enter in the phone number that you are at for that day. If you are always there give an option to remember device/number. That way as you are already logging into the softclient it should be able to pass your credentials on the backend for logging in or out.
