Keep in mind that the iPhone hardware isn’t that impressive, after you’ve been playing with PC’s. It will render triangles, a few of them at least, but certainly not the lush scenes you’re used to. Look at the existing 3-d iPhone apps–most of them have very limited 3-d geometry, just a few hundred polys or so in the foreground, and then a lot of flats in the background. Still, it will be fun to play with.
Note that an iPod touch might be a less expensive purchase option than a full iPhone.
David