In today's User Notes, Sarina Rosenberg recounts her experience with Verizon's V Cast Song ID.

I was skeptical when I first saw the ads for Verizon's V Cast Song ID. In the TV spots, a guy slickly uses his cell phone to identify the title and artist of a song he hears blasting from a convertible full of--you guessed it--flirtatious twenty-somethings. But this service is for real. Hear a song, open the application on your phone, identify it for free (some carriers charge a texting fee) and then pay ($1.99 per song on Verizon) to download it as a ring tone or MP3 file. Verizon offers the application, V Cast Song ID, on a slew of new phones, including the Chocolate, the enV by LG, the LG VX8700 and the VX9400 ($99.99-$199.99). Sony Ericsson announced their first phone with their music ID application, TrackID, in 2006, and some of the phones in the new Walkman series ($199-$499) come equipped with the application. Cingular and T-Mobile carry the Sony Ericsson line. Each service sets its own fees for the application.

Music recognition is finally going mainstream in the world of mobile. But the feature is simply a new twist on a relatively retro technology. These phones link to the same databases that supply the song information for applications like iTunes and Windows Media Player so that they can provide you with the artist, album and track information of a CD you slip into your laptop. Verizon's service uses the U.K.-based Shazam database; Sony Ericsson links to Gracenote.

In cell phones and laptops alike, the key to unlocking a song's identity lies in a six-second, incredibly specific music sample. "It's a finger-printing technology," says Ty Roberts, Gracenote's chief technology officer. Roberts explains it like this: as you hold your phone up to the music you want to identify, the phone's music-recognition application records a six second sound bite. It measures and records specific frequencies of the music down to the thousandth of a second. This is the fingerprint that the application then compares to the more than 60 million songs by more than a million artists in the Gracenote database. (Verizon uses a similar service, Shazam, and draws from a database of over 4 million songs.) And the fingerprints are so specific, Roberts says, that they differentiate between covers, live albums and studio recordings-miniscule variations like a new guitar, varying vocal quality and a slightly different drum line will all affect the "print." No two performances are exactly alike, Roberts says.

As magical as this may sound, the truth is that background noise can distort the "print." So managing to capture a usable sound bite can be tricky with these phones. In an informal test of Verizon's LG-VX8700 and the Sony Ericsson W710i Walkman, both phones required a strong, clear sampling. And you can't simply flip-and-identify like the Verizon ad suggests. It takes several seconds to open the applications on both phones, and even longer to capture the print. These services work well in confined spaces like cars, but they're unreliable and frustrating to use on the street. I wouldn't even attempt it in a crowded bar. But for those of us with the patience to wait for the recognition application to work its magic, these phones can indeed identify everything from Bach to Beyonce. They'll even match indigenous Brazilian folk, if you can get your hands on it.