Audicom IP Headset Adapter for 2.5mm Headset, RJ9/RJ10/RJ22 Headset Plug Adapter Converter for Aastra Adtran BT Alcatel Lucent Avaya Interquartz Lazerbuilt Ascom Telephone Phones (H25-STAB) 2.5mm headset jack adapter. Convert 2.5mm headset plug to some SPECIFIC phone models listed in the description. Save money by buying standard 2.5mm phone headsets to use with your phone's headset jack Reduce clutter with single headset Does not work with RJ11 jack, which is wider than your handset or headset jack (6 positions vs. 4). RJ11 jack is what is in the wall. RJ9, RJ10, RJ22 are what is on your phone handset or headset. NOTICE: Only Compatible With 2.5MM Headset And Some Specific Phones. Please see compatible phone models list in description below. Check our store for headset adapter for other phone models or Contact Us for Compatibility Guide!