I found that by pressing the Map button (1st on the left); it displays the map and switches back to the guidance mode, but the voice guidance commands are suppressed until you hang up.
Try it --
Getting 20 - 22 around town, and 25+ on long distance. Octane makes a difference. Average 2-3 mpg more using 92 or 93 than with 89. Are others seeing a difference with Octane rating??