The A10 cable (a.k.a. A10-16) can be used with any H-series headset to connect directly into a phone's headset port. When the A10 cable is used, no other amplifier is required.The A10-12 cable (PN 66267-01) has a 6 db louder transmit than the A10-16 cable. The A10-12 is designed primarily for use in Europe, New Zealand & Australia and may cause echoes on North American phones.