I'm no network engineer, BUT my basic understanding is that yes pausing the video would save data, as not as much info has to be transmitted. Now FaceTime audio, and a regular voice call are a different story. A regular voice call should use no data at all, but a FaceTime audio call would be voice over IP and it WOULD use data, BUT not use any of your plan phone minutes (IF you have limited phone minutes). But audio does use less data than video.