I've long been a fan of the Internet radio service Pandora—even more so since I got a car and discovered the joy of streaming music with it while on the go.

But now there's another free Internet radio service for the iPhone and iPad. It comes from a familiar face: Spotify, the popular online music streaming service that lets you listen to over 16 million tunes free with occasional advertising interruptions—or without ads, and with additional features, for a monthly fee.

Spotify added a free radio feature to its iPhone and iPad apps on Tuesday. The apps were previously meant for users of its premium service, which for $10 per month includes the ability to listen to on-demand tunes on your smart phone. With the radio feature, which already existed within Spotify's desktop computer software, Spotify becomes more alluring, and some of its nonpaying users may be convinced to sign up for its paid offerings.