... amplifier! They plug directly into your headset-ready telephone! What's in the box: Headset shown ... -Key Digital Feature Phones General Electric: GE Telephone Model 2-9451, 2-9490 GrandStream IP Phones ... 400, PLX-500 Packet8 Phones: 6753i, 6755i, 6757i Polycom: SoundPoint IP Phone Series, Models 300, 500 (rev. ... 5 or later), 550, 600, 650 POLYCOM IP300, IP301, IP430, IP450, IP500, IP501, IP600 & ...