My ZYXEL wireless gateway and BT analogue phone switch over to VOPI

I have a ZYXEL Wireless AC/N VDSL2 Gateway. Model VMG3925-B10C for my broadband. It works fine. BT are implementing a nationwide analogue phone switch off with telephone users having to use VOIP. I notice that friends who have BT supplied gateways like mine have a built in telephone socket on the back for VOIP. What equipment will I need to use a VOIP phone with my VMG3925-B10C ?