Recently I have been working with a Mitel 5330 IP phone. These phones have a port on the back for a headset.
I had an old plantronics headset laying around (not the amp, just the headset) and I hoped that by plugging it into the back, it would work for this phone. After all, one of the main features of this phone was the Headset-readiness.
That old Plantronics headset did not work. So I benched the idea for a while until I ran across a product on Amazon called the T100 Headset. This headset said it would work for VOIP Headset ready phones, so I gave it a try.
It seems to work pretty well. The sound is not as `full` as those with the amplifiers, but for $19.95 it was a great purchase. (Those amplifier types start at around $80)
Check it out from Amazon below.