Pandora Radio is an internet radio service, recommendation service, and the custodian of the Music Genome Project. Users enter a song or artist that they enjoy, and the service responds by playing selections that are musically similar. Users provide feedback on approval or disapproval of individual songs, which Pandora takes into account for future selections. While listening, users are offered the ability to buy the songs or albums at various online retailers. As part of the Music Genome Project, over 400 different musical attributes are considered when selecting the next song. These 400 attributes are combined into larger groups called focus traits. There are 2,000 focus traits. Examples of these are rhythm syncopation, key tonality, vocal harmonies, and displayed instrumental proficiency. The Music Genome Project is what powers Pandora's personalization, as it is a detailed, hand-built musical taxonomy. Using this musicological â€œDNAâ€ and constant listener feedback Pandora crafts personalized stations from the more than 800,000 songs that have been analyzed since the project began in January 2000. More than 75 million people throughout the United States listen to personalized radio stations for free on Pandora through their PCs, mobile phones and devices such as the iPad, and connected in-house devices ranging from TVs to set-top boxes to Blu-Ray players. Mobile technology has been a significant factor in the growth and popularity of Pandora, starting with the introduction of the Apple app store for the iPhone in the Summer of 2008. Pandora instantly became one of the most top downloaded apps and today, according to Nielsen, is one of the top five most popular apps across all smart-phone platforms. Pandora is mostly free and, thanks to connectivity, available everywhere consumers are â€“ at the office, at home, in the car and all points in between. In 2009 the Company announced that Pandora would be incorporated into the dashboard in Ford cars via SYNC technology; GM has already followed in announcing plans to integrate Pandora into its vehiclesâ€™ OnStar system. Since more than 50% of radio listening happens in the car, this was a crucial arena for Pandora. Also in 2009, Pandora announced that an agreement had been reached regarding the royalty issue, which would significantly reduce the royalty rate, making it possible for Pandora to stay in business. It announced, too, that free listening would be limited to 40 hours per month but can be extended to unlimited for that month for $0.99. "The revised royalties are quite high," the company's blog notes, "higher in fact than any other form of radio." The extended listening fee differs from "upgrading," which also disables advertisements, increases the bitrate to 192 kbps, and provides a dedicated music player (as opposed to listening through browser). This service, known as "Pandora One", costs $36 and is billed annually. Due to copyright and licensing rulings, Pandora is only available in the United States, but Pandora has said that it has plans to extend its service to a global market.