Its always tempting to go for the thing that you will get right away rather than wait, but you wont regret it if you wait till you can buy a car. an iphone will be old news after you've had it for a month, but I've been driving for about 10 years, and I've always needed/wanted my car.
Its more practical, and a much better investment. Plus look at it this way, if you lose/break your iphone, you are out of luck. cars at least have insurance. I have known many people that have dropped their expensive phones in the toilet, or somewhere else, and were just out of luck and had to buy another one.