UPDATE: Rock Band now pops up with this message declaring that all is well and to disregard the previous expiration message.

If you've been enjoying Rock Band for Apple's suite of iOS devices then I suggest that you spend all of the leftover enjoyment that you've been meaning to use on the game before the end of the month, because effective May 31, 2012, the app will expire and cease to work.  Mobile Rock Band fans are finding that the app is tossing out a casual little popup box warning that the game will no longer work come the end of the month and thanks players for "rocking out with us".  No explanation was offered for the shutdown, but the speculation is that publisher EA Mobile has come to the end of its licensing agreement for the songs contained within the iOS version of Rock Band.  Here's Polygon with the limited details:

In a comment on the Rock Band forum Harmonix community manager Aaron "HMXhenry" Trites states he has "No clue as to the specifics."

"My guess is that it has something to do with the MTV Games and EA logos that pop up when you load it. Since we are no longer partnered with them, I have no idea how that has affected projects like RB on iOS. But, as we've seen with the recent DLC delays, there's a lot of work being done behind the scenes now that Harmonix is independent and I wouldn't be surprised if this was related.

"Again, that's mostly guesswork, but I'm not at all familiar with the particulars of the partnership or how content is managed on iOS."

Electronic Arts has flipped the killswitch for parts of its games before (usually underplayed multiplayer modes in older sports titles), but breaking an entire game in this way is a new one for the company, I think.  Compounding the problem, Rock Band is still for sale on the App Store for $5.  There's no mention that this game is a dead app walking.  This sort of thing is why I still prefer old fashioned physical media that doesn't necessarily need an Internet connection when it comes to video games.  The old cartridges and discs of yesterday still work.  EA cannot swoop in and banish their, say, PlayStation 2 back catalog.  Revoking an iOS game, on the other hand, is a trivial exercise.  It makes me wonder how many other fun games and useful apps are a step away from being remotely wiped out by a publisher.  For some reason, my guess is that there are no refunds in this instance.  Thanks for rocking out with us!