I just installed a Pioneer AVIC F90BT nav in my Smart.
I didn't really do the install, it was done by Jason of
AVIC411.com He's a friend of my son and is an authority on Pioneer AVIC nav units. His website is the place to go for info on the Pioneer navs.
I ordered a double DIN bezel, a wiring harness, and an antenna adapter from Cruchfield. Other than some crimp connectors, the kit was all we needed. Tool wise he used a Torx 25 bit and a crimper. The installation took about an hour and it worked perfectly when we turned it on.
I was able to download this custom Smart splash screen off the avic411.com forums.
The AVIC unit is amazing. It pairs up with my iPhone via bluetooth, it can access music, playlists and even play videos. I'm still learning the navigation features. We're working on an installation video and some photos.