Other than accelerometer bug, the only fatal issue with the 4/4 build is WiFi not turning on.
The 4/6 update seems to work well, including the WI-FI. The only things I noticed not working are the screen rotation and accelerometer. As far as the speakerphone mic , I had a samsung stratosphere and it had two microphones in it, the Droid 4 only has one. would that possibly be the issue?