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.

•Making music. Smule's addictive 99-cent Ocarina turns the iPhone into the ancient flute-like instrument. You softly blow into the iPhone's microphone and play notes by pressing and holding your fingers over any of four virtual on-screen holes. There are 16 possible combinations, and you can alter the sound by tilting the phone. There's even "sheet music" on Smule's website to play anything from Over the Rainbow to If I Were a Rich Man.

Ocarina is social. Tap a globe icon to rate performances from users around the world. They, in turn, can show you the love.

Or try developer Benjamin McDowell's Harmonica app, also 99 cents. Sure, it's odd putting your mouth on the screen. Fortunately, you can also play with fingers.

•Diversions. I've enjoyed racing games that take advantage of the iPhone motion sensor, including Vivendi's Crash BandicootNitro Kart 3D ($5.99) and Pangea's Cro-Mag Rally ($1.99). I also like Glu Mobile's recent release of a 3D marble puzzle called Bonsai Blast ($3.99).

But as a casual gamer, I gravitate to titles such as Brain Toot (99 cents), which serves up vision, memory and other mind exercises. In one, while being timed, you must pick out the highest or lowest numbers from a series of numbers shown.

Semi Secret Software's $1.99 Wurdle is a wordsmith's addiction, kind of like Boggle on the iPhone. Against the clock, trace your finger across a letter-filled board to spot as many words as possible.

•Handy to have around. Want to convert kilometers to miles? Celsius to Fahrenheit? Fetch currency rates? Western ITS Limited's simple a2z Pro Unit Converter is free and a boon to folks who travel overseas.

The iPhone lacks a voice recorder. The 99-cent Retronyms Recorder adds the capability. There are a few ways to save recordings to a PC or Mac. You can e-mail a link or sync up recordings via Wi-Fi to listen in iTunes or another player.

Worried about adverse reactions? The free Epocrates Rx database can clue you in. You'll grapple with medical jargon, since Epocrates is aimed at health care pros. But the app can enlighten you about the drugs family members swallow. And if you've got a loose pill lying around, you might be able to identify it by entering its color, shape and other characteristics.

Looking for a new place to eat? Urbanspoon helps find restaurants near your GPS location. Shake the phone to spin three wheels, one representing neighborhood, the second, a food type, and the third, price. When the wheels stop, you've landed on a random listing with an eatery's phone number, address and reviews. The app is free.

Rather dine at home? The 99-cent Grocery IQ shopping list might help you bag the right ingredients. It has a 130,000-item database, right down to brand-name peanut butter, pretzels and pasta. You can choose quantities and sizes, and check everything off as you patrol the supermarket aisles. Or e-mail your list to whoever is shopping for you.

The free Google Mobile App has direct links to popular Google programs, including your Docs, News, Maps and location-aware search. Google also can search your phone's contacts, calendars and so on. The gee-whiz feature is Voice Search. Hold the phone up to your ear and bark out a query. Results aren't perfect. Google recognized a search for "child-friendly restaurants" as "cadence-friendly."

As part of its free app, Amazon is experimenting with an interesting feature called Amazon Remembers. You snap a picture of a product with the iPhone camera; photos are stored at the Amazon site. Amazon will try to find a similar product for sale on the Web, even at rival sites. It identified images I snapped of Bose headphones and the Sling Media SlingCatcher.

Need help hanging a picture? PosiMotion's 99-cent A Level utility works in landscape, portrait or face-up mode. As with a real spirit level, you try to position the iPhone so the bubble is aligned in the center of the screen.

Talk about not being on the level. You're on a blind date that's soured and are dying for an excuse to bolt. The aptly named 99-cent Fake Calls app from Magic Tap is your ticket outta there. You can select the time a fake call will come in, customize the "caller's" picture and choose a ring tone. You'll have to devise your own excuse for making an exit.