Get state of "talk" button through REST API

I am programming against a Calisto 7200 using the REST API that comes with Plantronics Hub. The device has a talk button, which seems to be used to pick up and hang up a call. Once pressed it lights up in red and once pressed again, the light turns off. When listening to the events, the only event fired is the "Talk" event. So it is hard to tell in what state the button is actually in and to synchronize the UI with the button. (As opposed to the the mute button for example, which sends a "MuteOn" and "MuteOff" event.) Is there a way to query the actual button state or am I doing something else wrong?