Personalized Internet radio services Pandora and Slacker are ending the year with new service offerings.

Pandora is making its mobile version available for free to Sprint wireless customers. The company previously charged $3 a month for Sprint customers to access the service. Under the new model, all existing and new Pandora users can stream their personal radio playlists at no charge from several models of Sprint mobile phones.

The Pandora service, which is one of the most popular music applications for the iPhone, is also now available to Windows Mobile smartphones, regardless of wireless operator.

The free version of the mobile Pandora app is ad-supported, with audio advertisements inserted into the music stream, similar to radio.

Meanwhile, Slacker introduced a new ad-free subscription tier, offering commercial-free streams for $4 a month when signing up to an annual plan. The subscription option allows users to skip an unlimited number of songs, something limited to six per hour per station with the ad-supported version, as well as build customer on-demand playlists as opposed to only random streams.