Last.fm and Pandora thought they had cornered the market in streaming audio on the iPhone , but they’ve got some serious competition in the newly launched Slacker application. Slacker, which may be familiar to Blackberry users, is a free radio application that contains more than 100 pre-programmed stations. The content also includes over 10,000 artist stations, biographies, album artwork and the ability to create custom stations.

Anyone interested in trying out Slacker should go to www.slacker.com on their iPhone or iPod Touch. This review suggests that Slacker is a “lot like satellite radio,” and mentions that it plays 30 second radio ads after every fifth song. This might be a small price to pay for most users, although Last.fm and Pandora offer uninterrupted listening. A premium subscription of $3.99 a month will remove all ads and allows you to skip songs with greater regularity than the free version.

It’s early days for these applications, but it will be interesting to see how Slacker fares in comparison to the well-established Pandora and Last.fm apps. "Our priority at Slacker has always been to give music lovers the best experience effortlessly," promises Marketing VP Jonathan Sasse. This site contains the full low down on Slacker for the iPhone.