It is not illegal to use such a feature. In some states ("multi-party consent" states), it is illegal to use the feature without the consent of the person bein

It is not illegal to use such a feature. In some states ("multi-party consent" states), it is illegal to use the feature without the consent of the person being recorded; just like in some situations it is illegal to use the "camera" feature without the consent of the person being recorded. That doesn't stop Apple for offering a camera on their phone. Other states have "one-party consent" laws that mean it is always legal for you to record own phone calls.