https://wccftech.com/android-8-1-att-pixel-2-oneplus-5t-oxygenos-4-7-4/

AT&T has rolled out a new update to the Pixel 2 and Pixel 2 XL phones today. The update is 531.7MB in size, and it brings the recently released Android 8.1 Oreo alongside AT&T’s in-house HD Voice functionality.

HD Voice feature makes use of noise cancellation and wide-band audio technology to enhance the call quality. For enabling the feature on the Pixel 2 after installing the update, users will need to head to Settings > Network & Internet > Mobile Networks and tap on the “Advanced Calling” toggle. However, it will only work in the areas that support the service.