Hi Harvey Specter Litt,

the headset has a built-in microphone that picks up your voice when you are on the phone. When you call or are called, you speak through the phone's microphone. The caller's voice can be heard through the headset. If you disconnect the headset cable from your smartphone or mobile phone, you can speak via the phone's microphone and loudspeaker.

Sony Europe

The WH-CH720N has a built-in mic. I often use it for team meetings. I don't know how the Sony can be used with a different mic. But presumably this can be set in the settings in Windows, Apple, etc.