The iTunes App Store is iPhone's killer app; free stuff

— -- 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.

And because of the drain on the battery, Apple still won't let developers produce apps that run in the background. So forget about listening to Internet radio while checking e-mail. I'm also waiting on an app that will let you shoot video.

All that said, exploring the App Store on your handheld or via computer is a delight, and you can rely on fellow users for reviews. Some of my favorites:

•Listening to radio. There's a reason Pandora has emerged as the most popular free iPhone application. Type a song or artist's name, and Pandora creates an instant radio station inspired by your selection, same as on a PC or Mac. Fine-tune stations by indicating whether you like what's being played. In some cases, you can buy the music you hear through iTunes.

The iPhone, of course, functions as an iPod. But your storage is limited. If you have gobs of music on your computer, consider Simplify Media. The $3.99 program lets you stream (most of) your music collection and that of up to 30 friends.

Setup is simple, and though music sometimes is slow to start up, it sounds good. Simplify generally worked really well as I rode in and around New York City. (It works on Wi-Fi, 3G or pokier Edge networks.) You can view song lyrics and artist bios. But Simplify can't remotely play iTunes purchases that are DRM or copy protected.

How often have you heard a song on the radio or in a club but didn't know its name? Hold the iPhone up to the radio, and let the free Shazam app identify the tune, usually within 20 seconds. Shazam doesn't get it right every time. But it correctly tagged material as varied as Come On Over from Isobel Campbell & Mark Lanegan and Corcovado from Astrud Gilberto.