A Westjet Boeing 737-700, registration C-FBWS performing flight WS-1402 from Calgary,AB (Canada) to Phoenix,AZ (USA) with 135 people on board, was enroute at FL390 about 100nm south of Salt Lake City,UT (USA) when the crew declared emergency reporting smoke in the cockpit. The aircraft diverted to Salt Lake City and landed safely on runway 34R about 23 minutes after leaving FL390. The Canadian TSB reported maintenance replaced an audio panel, a service difficulty report was filed.