If i belong to Verizone and my contract expires is a new cell cheaper?

My contract expires July 6th 2011 and i wan't the iPhone4 and currently have the CRAPPY enV touch and after my contract expires would i be do for like an upgrade and get the iphone cheaper or not and if not when will i be due for an upgrade and what is an upgrade im very confused i just really wan't the iPhone oh and im not tech. retard i just dont get the whole contract phone upgrade system thing!