Direct Connect Headsets require phones that have a separate modular (phone size jack) port with a headset symbol above/below them. NOTE*** Please refer to the list of phone manufacturers to the side and below to narrow your search.
Headsets for your Avaya AT&T Lucent office phones and telephones.
Headsets for your Cisco Telephone and IP phones
Headsets for your Nortel office and Nortel IP phones