Headphones won't connect?

Hi. I got the iPhone 4 a few days ago and put an otter box on it immediately I just tried plugging my apple headphones in it for the first time, and they don't fit completely. They pop right back out and will only play music through them if you hold them down. I tried a different pair of headphones and the same thing happened. I checked for lint with a toothpick and there is none. The phone is literally brand new..