iPhone is the hottest desirable gizmo at this point of time. As per AppleInsider (http://www.appleinsider.com/article.php?id=2415), Apple is going to make 47% – 49% margin on each iPhone sold.
So, if you are not in a big hurry, waiting for a few months might save you some bucks. With so much of margins available, Apple will definitely try to push iPhone hard to gain some marketshare of the fiercely competitive mobile phone market. They will do this sonner as they are already a late entrant and it has to cover a lot of ground to be considered as a serious competition for established mobile phone companies like Nokia, Motorola and Sony Erricson.
Being a second mover will also give you inputs from the early adopters, making your purchase risk free. Good things come to people who wait (well a little cheaper).