Polycom IP phones are a little troublesome when it comes to headset compatibility

If you have a Polycom Soundpoint IP phone such as the Polycom 300, 301, 430, 500, 501, 550, 600 (rev. E or later), 601, 650 or 670, you'll want to read on.

The good news is that these phones are headset-ready so you can simply plug a headset right into the dedicated headset port BUT (and that's a big BUT), most of them will give you a nasty buzz sound. The only model that Plantronics has successfully tested and recommended is the Supra Plus with the Polaris cable. There are several Supra Plus models to choose from but they are all headband style (so if you are an ear hook person you are, unfortunately, out of luck).

Here's the link for all the appropriate headsets and the cable for you to consider:

http://www.founderstelecom.com/posoipphmo50.html