Using PC headphone/mic with telephone socket
 

Our office recently migrated to Cisco 7491 VOIP phones. Our old phones let us use the headset/microphone sets you buy for a computer as a headset. It had a socket for the standard micro (?) plug. These new phones have a standard phone socket (I guess RJ-11?) and the only option we've found so far are the Plantronics headsets. At $100 each the company is not going to be purchasing them for everyone. I'm wondering if anyone knows of an adapter that will let you plug a headset with a micro plug into an RJ-11 socket and get both voice and audio enabled.