The killer app for the iPhone is — drum roll, please — the iTunes App Store. Five months after Apple launched its online emporium, I believe it even more, having downloaded a gaggle of programs, including some that transform my iPhone 3G into a harmonica, metric system converter and level. There are now more than 10,000 of these applications for the original iPhone, its 3G successor and, in most cases, for the iPod touch. Many are free. I encounter buggy programs from time to time, but there are frequent updates to fix such snags.
