I've just tried tuning into DI.fm, but a message keeps repeating all the time.

Here's what I found on savenetradio.org:

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The Day of Silence on June 26th

The regularly scheduled programming of millions of Internet radio listeners will be temporarily interrupted tomorrow when tens of thousands of U.S. webcasters observe a national Day of Silence. Protesting the recent 300 percent royalty rate increase for online music webcasters, the aim of the industry wide daylong blackout is to raise awareness of the threat these new rates pose to the future of Internet radio and rally support for legislation pending in Congress.

"Webcasters of every size and from every corner of the country will stand united tomorrow to protest a very real and fast approaching threat to their livelihood,” said Jake Ward, a spokesperson for the SaveNetRadio Coalition. “With nearly a half million emails and phone calls from webcasters, listeners, and the artists they support sent to Congress in just the last two months, this national grassroots campaign has certainly captured the attention of lawmakers, but there is more to be done and time is running out.

During the National Day of Silence webcasters will urge their listeners to contact their congressional representatives and ask them to support the Internet Radio Equality Act and preserve the future of Internet radio. Tomorrow the silence of tens of thousand of webcasters will make the call to save Internet radio heard loud and clear. Internet-only webcasters and broadcasters that simulcast online will alert their listeners that "silence" is what Internet radio may be reduced to after July 15th, the day on which 17 months' worth of retroactive royalty payments -- at new, exceedlingly high rates -- are due to the SoundExchange collection organization, following a recent Copyright Royalty Board (CRB) decision.
http://www.savenetradio.org/