The founders of two of the Internet’s highest profile ventures are getting into the music business.Janus Friis and Niklas Zennstrom, co-founders of Kazaa and Skype, are teaming once again to unveil Rdio (pronounced “r-dee-o”), which kicks off a limited launch today. The service aims to blend social media, online music and portability. With applications for the Blackberry and iPhone (and, soon, Android), Rdio will give subscribers unrestricted access to its entire music catalog of more than five million songs, with artists from EMI Music, Sony Music Entertainment, Universal Music Group and Warner Music Group, and a number of indie aggregators. Fees will run $9.99 per month for Web and mobile access or $4.99 per month for Web-only access. While subscription music services are nothing new — Napster and Microsoft both offer services with some similar features — Rdio hopes to stand out by utilizing cloud technology that stores user playlists and song selections on a central server. This allows people to begin listening to a playlist via the Web on their desktop computers, then pick up exactly from where they left off on their mobile devices. The service will also help users discover new music by using Twitter-like functionality, letting people monitor what others are listening to and putting it on their playlists.