|(Updated with AppleInsider info) Buried code in iOS 6.1 may hint at a future radio feature, notes 9to5Mac. After applying the evasi0n jailbreak, the site says it discovered code for a radio button hidden in the iPad Music app, even though the app is only equipped to play local files or content from iTunes Match. One possibility is that Apple is planning to implement support for Internet broadcasts, as with the desktop version of iTunes.
The button files also contain the word "buy" in their names though, which may suggest they're related to Apple's long-rumored subscription service. Apple has reportedly been talking to music labels about the prospect for some time, and last October, Bloomberg indicated that the service could launch this quarter. The new iOS 6.1 content may imply that Apple is at least laying the groundwork for a service, the launch of which would be contingent on securing label deals.
Conspicuously, the buttons don't appear anywhere in the iPhone version of the Music app. It's unsure why, but that could simply be reflective of how early a radio feature is in development.
Update: AppleInsider has gone into further detail, noting that the filenames all begin with "transport-radio," and modify the button for four different states. These include "black," "pressed gray," "confirm," and "confirm pressed." The significance of the term "transport" isn't known, but could possibly refer to the name of an Apple service.