... and extremely comfortable fit design for all-day use. Only compatible with telephones with a built-in amplifier. Some specific models: 3Com: 3102 ... , 4620, 4621 5410, 5420 5610, 5620 DT1, DT3, DT5 Cable & Wireless: CWB 100H, CWB 200H, CWB 500, CWB 600 Comdial: 8312 ... , DKT-3014SDL, DKT-3020S, DKT-3020SD( MUST HAVE TOSHIBA?BHEU ADAPTER for on hook answering, sold by Toshiba, not available from ...