Tired of waiting for Apple's iPhone? You might want to check out a potential rival that you can buy sooner: Samsung's innovative, super-slim, two-faced UpStage (M620), sold by Sprint Nextel.

On the eve of the giant CTIA Wireless trade show here in Orlando, Florida, Sprint announced that it will begin selling the UpStage on April 1. Its price will be $300--or $150 with a two-year contract, Sprint representatives say.

Unveiled in January at the Consumer Electronics Show, the UpStage is a candy bar-style handset that's less than half an inch thick and not much taller or wider than an iPod Nano. While other multimedia-friendly cell phones struggle to balance the sometimes-conflicting requirements of a conventional handset and a music or video player, the UpStage solves this quandary by putting phone functions on one side of the device and multimedia functions on the other.

The UpStage's phone face has a 1.4-inch sliver of a color screen, a directional toggle, and a keypad arrayed with soft, flat keys. The music-player/multimedia side of the device features a 2.1-inch, 176-by-220-pixel display and a touch-sensitive navigation pad with a central button. A small Flip button on the edge of the unit toggles between the two sides, but the prompt to confirm that you want to stop playing music (on the music side of the phone) and instead make a phone call gets old pretty quick. (The phone side of course springs to life for incoming calls, halting music playback; the music resumes once you disengage the call.)

The UpStage felt small but solid in my hand; I found its keypad quite usable, and the sound quality on voice calls was generally good. The four-way capacitive touchpad on the music side has a central, mechanical play button that took some getting used to. The excellent documentation (including a printed manual of over 300 pages) warns against trying to swipe it in a circle the way you would an iPod's control wheel, but the temptation is hard to resist. It also took me a while to stop trying to use the central button for directional navigation (instead of tapping the touchpad above, below, or on either side of the button).

Even when the music/multimedia side is activated, you have to use the phone side whenever you need to input text--for example, to create a playlist, to search the Sprint Store's music catalog, or to specify a URL for a site you wish to visit in the small-screen-optimized browser.

I was a little confused the first time I encountered a text-input box on the music side, since no alphanumeric keys and no software keyboard appeared. But the device is smart enough to recognize the need to use the phone side, and I noticed that 'Flip' had appeared on screen as a soft-key option.

When I used it and began entering text from the phone keypad (T9 text input mode is a welcome option here), 'Save/Flip' also appeared as a soft-key option to return me seamlessly to the multimedia side.

When you first flip to the music side, the UpStage screen (outfitted with rather unattractive wallpaper that looks like a still from one of those iPod animated TV ads) displays three icons. By default, the central icon is highlighted; this musical note icon activates the phone's player functions. To its left is a small PC icon for invoking the phone's syncing mode, and to the right is a dollar sign (appropriate choice!) that gets you to the Sprint music store for acquiring tunes over the air.

In syncing mode, you can transfer music from a PC to a microSD Card that you slide into a slot below the Flip button. (The phone comes with a 64MB starter card, and it can support cards with capacities up to 2GB.) First, however, you must install and run the included Sprint Music Manager desktop application and connect the phone to your PC using the included USB cable. Only then will you be ready to select the 'Sync My Music' icon.

The Sprint desktop application is reasonably intuitive to use, though it's no Windows Media Center or iTunes killer. When you launch it, it searches for and builds a library of your MP3, Windows Media, and WAV tunes. (The phone can import non-copy-protected files in all of these formats; Sprint says that it will convert Windows Media files without DRM to AAC+ format before uploading them to the UpStage.)

Once the phone is connected to the PC, you simply drag and drop tunes (or albums) from the desktop app's left-hand pane to a lower-right pane. The application will check whether the memory card has enough free space to store the tunes you've selected; if not, it won't start transferring files until you've winnowed down your list so the music fits. You can create playlists on the phone itself.

In the connected mode, you can also use the desktop software to play music from the phone, or to transfer tunes you've purchased from the Sprint store to your desktop. But don't expect great quality from these tracks: The music is recorded at a very low bit rate in the expectation that they'll be played primarily on a phone.

As someone who has spent a fair amount of money on high-quality music earphones, I appreciated Sprint's decision to substitute an earphone adapter (complete with a microphone) for the usual mediocre-quality earbuds. I happily plugged my Etymotics earbuds into the adapter, and I got great-sounding audio for both music and voice. A clothes clip on the adapter solves the problem of the microphone dangling fairly far from your mouth after you plug in your own headphones.

Another of the UpStage's innovative features: A stylish flip case with an embedded battery (Samsung calls the case a wallet). The case's purpose is both to protect the two-sided phone's screens and to help prolong the phone's useful life between charges.

The phone slides into the wallet and fits into a rigid cradle at the hinge. The included charging cable charges both the phone's battery and the wallet's battery. When stored in the wallet, the phone recharges itself from the wallet's battery. Sprint and Samsung's fact sheet says the phone's battery will support 2.5 hours of continuous talk time, which rises to 6.3 hours with the help of the battery wallet. We'll update this story--and provide our PCW Rating for the phone--once the PC World Test Center completes its independent battery life tests.

Of course, the battery gets sapped more quickly if you make heavy use of Sprint Power Vision features such as Sprint TV, which provides access to an assortment of free and for-a-fee video clips (all incoming phone calls roll over to voice mail while you're using the video service).

The UpStage includes a 1.3-megapixel camera with tools that let you adjust brightness, optimize photos of handwriting (for digital "postcards"), add a frame to an image, and the like. The camera can also capture MP4 video at 15 frames per second (in clips running for up to 30 seconds).

In addition, the UpStage comes with support for subscribing to and listening to mobile podcasts via VoiceIndigo's free mobile service. You can also initiate calls to contacts, using Sprint's Voice Command service. The phone's Bluetooth radio supports headsets and hands-free kits, too--and you can use it as a PC modem.

Could the UpStage seriously challenge the as-yet unreleased iPhone? That remains to be seen. The UpStage has some drawbacks: Its screen is on the small side for video viewing, and without a QWERTY keyboard, it falls short as a serious device for messaging or e-mail.

Then again, the iPhone's innovative software keyboard has yet to prove itself in the field, and the UpStage is a lot more affordable. If you're a music lover for whom video, e-mail, and messaging aren't top priorities, you might find the Samsung approach really does upstage Apple's.