Problem #1: When I'm in my car, my phone always seems to find it's way into the cup holder. Unfortunately, this means whatever nastiness resides in the cup holder finds it's way onto my phone.
Problem #2: My phone isn't charging when I throw it into the cup holder.
Solution: Create a phone dock that sits in my cup holder that charges my phone.
After-The-Fact-Problem: My Android phone doesn't go into car mode when I dock it into my Cup Holder Phone Dock.
After-The-Fact-Solution: Put an NFC sticker on the dock's back rest, and write an Android app that puts the phone into "car mode" whenever the tag is detected.
Note: This dock is for a Galaxy Nexus, but you can adapt it for any phone if you have the OpenSCAD chops!