How can I contact apple to suggest a new feature for the iPhone 4?

The iPhone 4s death grip is one thing, but what’s even worse is the proximity sensor. It’s what turns the screen off while you are on a call. It’s terrible. Screen is always turning on, pushing buttons with yr cheek. Hold, speaker, even end call!!! What we need is the ability to lock the screen. While in call – hit the sleep/wake button to lock screen. Then hit it again or the home key to unlock or another slide to unlock. Something! If we all ask they will do it.