I have an 06 TL w/ navigation.
Issue: Unfortunately, when I moved to HI the navigation no longer works and there isn't an update to include Oahu. My options were get a 1. new in-dash navi, 2. replace with 2007-2008 navigation or 3. hardwire portable navi
Solution: #3 Hardwired Garmin to give a similar look to Mazda 3 or BMW navi. Total cost= $360 (Drivesmart 61 plus materials)
Process:

1. Drilled hole in dash to pull the power cord through.
2. Used an add-a-fuse and socket in the fuse box area (driver side)
3. Mounted navigation with 3M and Sugru (moldable rubber found at Target or Amazon)

Result:

1. 6.95" Touch/ Voice activated navigation w/ traffic.
2. Powers on and off with ignition
3. No visible cords
4. View is not blocked

This may not be for everyone because you do lose the top center screen w/ clock and temp, but for me it was worth it to have navigation.

View from outside. I think much better than the Garmin mount.
Another shot of the setup.

 

Great functional addition....I would be more worried about the temptation for it to be permanently "borrowed" when out and about.

 

Yeah, "borrowing" is always a possibility/concern. I'm hoping the fact that there are no wires and it is firmly attached to the dash will be a deterrent, i.e. can't snatch-n-go like a suction mount GPS.