The smart money on tomorrow's mysterious iTunes announcement is that Apple will finally be adding the Beatles catalog to the digital music store.

That's not fully confirmed, but after a day of phone calls, e-mails and cryptic messages, Billboard.biz is sticking its neck out and saying this is what we're going to hear tomorrow.

It wouldn't be the first time that Apple was "on the verge" of announcing a Beatles deal. For years, every music-related announcement coming from Apple carried a hint of maybe "today's the day." But this time it's very likely that it'll be the case tomorrow morning.

Apple Promises Big iTunes Announcement Tuesday: 7 Possibilities

For starters, the sources in the past that quashed any rumors of an impending Beatles launch are today very quiet, and strangely so. Next is the wording of the teaser on Apple's website. The first line is, "Tomorrow is just another day." As noted earlier, "Another Day" is a Paul McCartney song released on his solo record "Ram," but written during the Beatles' "Let it Be" sessions.

Also, for those into hunting for more clues, Apple's teaser page features four clocks, each with the arms in different positions, (denoting the time of the announcement in California, New York, London and Tokyo time zones). Pretty unnecessary unless you compare it to the cover of the Beatles' "Help!" album, featuring all four members side by side with their arms also in different positions.

For these (admittedly thin) reasons and others that we can't yet divulge here, place your bets on a Beatles announcement tomorrow. Now comes the speculation as to what that announcement will entail.

Other than the obvious, which is that all the Beatles songs will be available for a la carte track-by-track sale in iTunes, there will almost certainly be some kind of additional offers in play. We're expecting some kind of device integration, perhaps a Beatles-branded iPod or iPhone -- or even an iPad that comes with the entire Beatles catalog pre-loaded for some astronomical price. We think all the Beatles movies available to buy or rent. We're also hoping (but not too strongly) for some amazing iTunes LP or iPad-related special treatment of all the Beatles songs for a more immersive experience on that includes all sorts of multimedia from the Beatles archives, including lyrics and video.

This will almost certainly be an iTunes exclusive for a period of time, after which hopefully the floodgates open and every other digital music retailer and streaming service will also have access to the valuable archives of Beatles music.

Now skeptics would rightfully ask whether adding the Beatles to iTunes will indeed be a day "that you'll never forget," which is what the Apple teaser promises. Apple CEO Steve Jobs is a huge Beatles fan, and has wanted to add the Fab Four's catalog for some time. So it's certainly a day he will never forget. And Jobs has ways of introducing new products and services that we never forget either.