Slacker Radio wants more BlackBerry customers to use its Internet-radio service, and it will be covering the hardware costs of BlackBerry Curves on the four major U.S. carriers.

The company is having this promotion to celebrate the success of its BlackBerry application, as it said more than one million customers have downloaded Slacker. AT&T users can get the Curve 8310, Sprint Nextel and Verizon Wireless subscribers can get the Curve 8330, and T-Mobile customers can nab a Curve 8320.

Users do have to sign up for a carrier's two-year voice plan of at least $39.99 per month along with a monthly data plan, which can cost an additional $20 to $30 per month. Additionally, users will be hit with a $36 activation fee and a credit check. The handsets are relatively old models, as RIM has already released updated Curve smartphones for AT&T and T-Mobile. Most of the Curve handsets Slacker is offering can be had for about $50 without the promotion and with a new contract.

Slacker is an Internet radio provider that enables users to listen to music or spoken-word audio based on the genre or artist of their choosing. Unlike rival Pandora, Slacker enables users to cache songs on the phone's memory to continue playback when there's no mobile data connectivity. The company recently received a high-profile boost as Verizon pushed its application to BlackBerry Storm and Tour users.

The success of the Slacker app is a strong signal that Research In Motion is gaining traction in the casual, or "prosumer" market. During its last quarterly earnings report, RIM said more than 45% of its approximately 28.5 million subscribers were non-enterprise users.

Most companies are just starting the hard work of mobilizing workforces by bringing the software they use to smartphones. InformationWeek analyzed this issue in an independent report, and it can be downloaded here (registration required).