Ford, Honda and Subaru all announced partnerships with Internet radio providers this week at CES, promising digital and custom user-created radio stations and other web content into their vehicles by leveraging the user’s smart phone and a free downloadable app.

Honda and Subaru plan to offer Aha radio in upcoming models. Honda hasn’t announced details, but Subaru says Aha will provide access to tens of thousands of stations, including on on-demand music from MOG and Rhapsody; Internet radio from Shoutcast, CBS, and Slacker; live news; podcasts from NPR and others; free audio books; personalized traffic reports; Facebook and Twitter news feeds; and user restaurant reviews and recommendations from Yelp.

Subaru Aha operation will be integrated into the controls of an optional built-in audio system. The free Aha app for the iPhone is available now in iTunes; and Android version is promised in early 2012. Subaru has not released specifics regarding availability and cost.

Meanwhile, Ford has partnered with iHeartRadio, to bring some 800 live and digital stations into vehicles, along with user generated content. Accessed through SYNC with AppLink, Ford owners will have the option of operating the radio through voice or steering-wheel mounted controls.

The Ford option will let drivers and passengers do everything from creating a custom station and stopping or starting a song to playing local iHeartRadio stations and finding traffic reports. The system lets users ask for programming by genre, city, or personality to access the type of programming or host they’re in the mood for. IHeartRadio also lets users share music with friends hands-free on Facebook Timelines using SYNC AppLink.

The SYNC-enabled iHeartRadio app is available now through iTunes and BlackBerry App World, and is coming soon to the Android Market.

One thing is sure: If you’re planning on streaming internet radio in your car for any length of time, you’d better have an unlimited or at least very large data plan with your cell-service provider.

Expect more carmakers to offer access to Internet radio soon. It remains to be seen how easy these systems will be to use, and what heir impact on distracted driving will be. Neither Ford nor Subaru has specified how much functionality will be available to drivers while the vehicle is in motion.