Just got my 300h a few hours ago. My nav prompts come from the driver speaker and are over the radio. The radio only seems to mute for phone calls or when hitting the voice button. I did see a setting to turn up the voice volume if it's not loud enough for you. Mine is on 2 and it seems loud enough with a moderate radio level.
I had a 2008 IS and a 2010 HS that both muted navigation prompts while on phone, and temporarily muted radio when prompts came up. Shocked in my new 2013 ES300h that prompts continue to play while you are on phone, and no stereo muting. People on the other line think the navigation prompts are speaking to them, and keep saying "What?"
This is ridiculous and a major disappoint for a more expensive car. Shame on Lexus.
Please submit feedback to 1-800-25-LEXUS (1-800-255-3987) prompt #5. it took less than 5 minutes. She said once a certain feedback threshold is met, then the will consider adding suggested changes to a firmware upgrade.
Our dealer is having a welcoming reception for new owners next week and I am preparing a list of questions. This topic will be on it. As I mentioned above, with the voice system on my 2011 MDX I can change XM stations or any stations, as well as select artists or songs on the hard drive that is built in. I will be surprised if the Lexus cannot do this.
My dealer as well is having a seminar on February 13th. I intend to resolve the NAV mute question as well as others at the meeting. Report to follow.
Thank you for bringing this up with your dealers! Please report back any findings or discussion. Make sure they understand IS and HS models do this correctly, so the technology is there. It is likely a software update.
My dealer's gathering turned out to be dinner, wine, a presentation, and a car wash. The gathering was so large that the service and technical folks were assisting in car wash & valet so there was not a good time to get questions answered. I am going to set a time in a week or so with one of the technical team to get trained and will ask questions then (this is my wife's daily drive so she was previously educated on the car).