Do you know what the IPhone app is called?

Okay, so I have an IPhone and the Home.Return/Button goes crazy once in a while~ It doesnt work all the time so I have to turn it off then on to get to the main page. A friend of mine told me there is an app for a home/return button but sadly, I havent found it:'( Anyone know what its called??? (Btw I have a IPhone 3g (My friend moved to another country so yeah and I cba to return it)) Pls Help xx