Hi Timothy, you may purchase it outside of RingCentral. We do not sell an expansion module; we only sell desk phones with a built-in expansion module.

Seeing Mary's answer - I can say that we've had good results from: https://www.metrolinedirect.com/polycom1.html when we went from Avaya to updated Yealinks and Polycoms.

We've bought over the years and each order has been fine. They're quick to answer questions, and fairly quick to ship.

Hope that helps.