Just to address a few items on device use:

This often is because your ear is hitting the button for speaker on the touch screen. I had this happen on my phone a few times while a friend was using it to talk to someone. I was puzzled, because it never happened to me, but seemed to happen to him regularly. I figured it out by watching him use it a few times.

The problem stemmed from the fact that he was reluctant to press the phone to his head, which caused the proximity sensor to not trigger properly. The result being as he was holding it slightly away from his head as he was walking along. This also caused the back light to flicker on and off as the touch screen enabled and disabled with proximity to his head. Since the change isn't instant, it occasionally was on as the screen headed toward and touched his ear, and *bomp* his ear hit speaker phone and it started blaring.

I could imagine this happening if you have a screen protector cover over the proximity sensor, or if you hold the device at a funny angle. (Or possibly if you have oddly shaped ears?)

Contacts take a while to load from the phone app:

I honestly didn't know about this until someone mentioned it and I tried it. I does take a while, and I'm not sure why. I blame portrait mode.
I've never hit this issue, since when I've wanted to call someone, I would simply look them up in the contact app by typing a letter or two on the keyboard while on the desktop. This brings up the contact list filtered to those with a first or last name matching the typed letters. For example, if I type ch I get:
Christopher Mains
Charles Yost
Jenifer Christmas
Markus Champion

I then tap their name, and tap the phone or sms button to call or text them. (Or the Yahoo, AIM, Facebook, or Skype buttons to IM, or their email address to mail them, etc).

I don't think I've ever opened the phone app directly except to see my call history, which I've usually done via the task manager when I have a yellow "missed call" page.

So, some of the issues may be circumvented by changing how you use the device, or you may not even have the issue if you use the device differently than another person.