Movie release windows continue to change before our very eyes. Bad Teacher -- the raunchy comedy starring Cameron Diaz, Justin Timberlake, and Jason Segal -- is being made available digitally now, ahead of next Tuesday's DVD release.

Variety claims this is the first time a major movie studio has gone this route, but there's a method to Sony's (NYSE: SNE) madness.

Head out to Amazon.com's (Nasdaq: AMZN) video storefront and the movie is available as a $14.99 digital purchase right now. Web-savvy couch potatoes who prefer the $3.99 rental option will have to wait until Tuesday.

Yes, it's only digital purchases that are jumping the optical disc gun. The plan here is to get folks to embrace ownership over rentals, as it's more lucrative to the studios.

Bad Teacher is now available through Amazon, Apple's (Nasdaq: AAPL) iTunes, Wal-Mart's (NYSE: WMT) Vudu, Microsoft's (Nasdaq: MSFT) Xbox, and Sony's own PlayStation Network.

Studios and distributors are doing a lot of experimenting with release windows these days. Comcast (Nasdaq: CMCSA) is testing a ridiculous $59.99 price point next month for a movie that is still playing at the local multiplex. DIRECTV (NYSE: DTV) has been offering a similar service at half of Comcast's price for movies, 60 days after they begin their theatrical screenings.

Since digital consumers are apparently flocking to cheaper rentals, we can almost view Sony's move as another attempt at offering early access at a premium. We'll see how this pans out. The studio will obviously be watching to see if an early digital release has a negative effect on DVD sales next week, but it's a test worth trying given the sluggish optical disc market these days.

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