new iPhone owner!

Well, I didn't get the new 4S, just jumped on the great deal for the iPhone 4 for only $99.

This is my first iPhone, I was always on Verizon so I wasn't able to use one for a while. Now that my contract was up I dropped the Android device and went for the iPhone. I do have one question though. It seems that at times, whenever I make a phone call, the display doesn't go to sleep after putting the phone up to my ear. I'm wondering if it's the case that I got at Verizon is preventing this? Kind of confused about that. I have also had two calls since I've gotten the phone, where after about a couple of minutes, they couldn't hear me on the other end. I'm wondering if this is because I was currently connected to my wifi at home? Myself and the person I was talking to both had great reception. I was able to call them back and carry on the conversation with no problems. Other than that this thing is great! Any ideas?

EDIT: You know what? I just thought about something, I'm willing to bet that my cheek hit the mute button, and that's why they couldn't hear me.