The Internet's tentacles seem to have no limit, reaching out and strangling everything from CDs and book stores to newspapers and magazines. Now it has its sights set on the car radio.

Many people are already accustomed to plugging an iPod into the car to listen to their library of Chet Baker or Arcade Fire tracks rather than CDs. And many vehicles have auxiliary plugs and USB ports to accommodate digital music fans. But now a new movement is afoot that could really threaten traditional broadcast radio: Internet music services such as Pandora, Slacker, and Last.fm--already popular with computer and smart phone owners--are being tailored by software developers, consumer electronics companies, and even auto makers to work more seamlessly with car stereo systems. So, while video didn't end up killing the radio star, this time the Internet might just succeed.

The devices responsible for this trend are smart phones like Apple's iPhone, RIM's line of Blackberries, and phones based on Google's Android software. These handsets all have free applications that play customized music channels streamed over the Internet using the phone's 3G wireless data connection. The services are generally free, although smart phone owners typically pay about $30 a month on top of regular voice service for unlimited data usage.

The attraction is that rather than being shackled to the same old hits from local radio stations, music fans can customize the music channel to suit their individual tastes. Pandora boasts about 750,000 songs and 40 million listeners. Put in the name of your favorite artist, say Chairlift, and Pandora creates a station that features Chairlift and similar groups, such as Metric.

But until now using such a service on a phone in the car meant looking away from the road to switch channels or skip a song on the phone--a major distraction. So companies are now marrying these services to existing in-car controls, essentially making it no different from switching between 1010WINS and Q104.3.

Car stereo maker Alpine, for example, offers the $400 Alpine iDA-X305S Digital Media Receiver with Pandora Link. Using a special iPhone-compatible cable, the in-dash receiver lets listeners skip through their customized stations and even give songs a thumbs up or thumbs down by pushing in and turning the receiver's front dial. The downside is that drivers still have to look down at the stereo's display to find what can be a needle in a haystack of endless channel choices.

Pioneer recently introduced a more elegant solution that adds voice control to its Pandora option. The AVIC X920BT costs $1,200 (plus the price of a professional installation), but it throws everything into one package: a 6.1-inch LCD touch screen, turn-by-turn navigation, AM/FM/CD, and carbon-conscious features such as an Eco Graph display that tells you how your driving habits are hurting (or helping) the planet. But plug in an iPhone to the system using an optional $50 cable, and it really shines. Not only will the in-dash display list your iPhone music library but it also controls an about-to-be-released Pandora app specifically designed to work with the Pioneer system.

During a test drive....(radio stations respond).