Why does my iphone home button not work sometimes? Can I have my iphone replaced?

I've had my iphone 4 for about a year and a half. The button that takes me back to home sticks sometimes, like ill have to hold it down a really really long time until it takes me to voice control then ill cancel then hold down the button for 6 seconds again then it will take me back to home from whatever app i was on such as texting. Its a process and sometimes even that doesn't work, sometimes i have to turn my phone off and on to get back to home to continue on to do what i wanted. Why does this happen? Like why does the button stick all the time?
sometimes the button will work perfectly fine, for about an hour… Then the rest of the day to a week it will be frustrating and annoying.
i have a 2 year contract on the phone and its up in May. I have insurance on the phone too, and i'm wondering if the insurance covers this issue i'm having… Like could my phone be replaced?

That happened to me too but on my iPod Touch. Here's what you do:
1. Settings