The A10 cable (a.k.a. A10-16) can be used with any H-series headset to connect directly into a phone&#39;s headset port.  When the A10 cable is used no other amplifier is required.&lt;br /&gt;&lt;br /&gt;A10 Direct Connect Cable:&lt;br /&gt;Easily connect any Plantronics H-series headset to a headset-ready phone via the headset port with A10.&lt;br /&gt;&lt;br /&gt;Recommended for use in an environment with a mix of M22 amplifiers and direct connect solutions.*&lt;br /&gt;&lt;br /&gt;Allows H tops to be used in amplified and direct connect systems  and  reduces the risk that the wrong headset will be connected (Polaris on an M22 or H top on a U10P) which would result in degraded transmit.