The big problem with music subscription services has always been the risk of losing the ability to play your favorite tracks. Sure, you get unlimited access to a big catalog, for a flat monthly fee. But if you stop paying, or switch to an incompatible music device, poof, there goes your music.

Microsoft thinks it has come up with a compromise. Users of the company's Zune Pass music subscription service will now be able to choose up to 10 tracks a month to add to their permanent music collections -- theirs to keep and play even if they stop subscribing. Microsoft is unveiling the plan tonight.

Is this the moment Microsoft's Zune device finally becomes a serious iPod challenger? No, it's probably going to take a lot more than this. But it's a sign that the company is still willing to get creative in its bid to chip away at Apple's dominance of digital music.

Microsoft will offer the 10 monthly permanent tracks as a free addition to the $14.99-a-month Zune Pass subscription. The company says it negotiated deals with major labels EMI Music, Sony BMG, Universal Music Group and Warner Music Group, and independent music distributors, to offer the enhanced service.

Each month, Zune Pass users will get credits to download to their permanent collections 10 tracks they choose from among the millions of tracks in the Zune Marketplace.

One catch: The credits will not roll over. If someone uses only eight credits in a month, for example, that person will start the next period with 10 credits, not twelve.

Most of the available music will be in MP3 format, free of digital-rights management (DRM) limitations, said Adam Sohn, director of Zune marketing. Others will come with DRM that may limit the number of PCs and devices the songs can be played on.

But in either case, the selected songs in a permanent collection will remain playable even if a user lets the Zune Pass subscription expire.

"We've said for a long time that we didn't think the current set of subscription models were the right formula, and we've been pushing hard to look at different models," Sohn said. "The labels have actually been super-cooperative with us on this stuff, and we're pretty excited to get it out there."

Microsoft didn't disclose financial terms of its deals with the big labels. However, the pacts aren't exclusive. Microsoft's agreements with the big labels wouldn't preclude them from striking similar deals with Apple or other music services. Other big music subscription services in the market include Rhapsody from Seattle-based RealNetworks.

Apple CEO Steve Jobs has historically pooh-poohed the notion of music subscription services, favoring the traditional a-la-carte and digital album purchases available through Apple's iTunes store.

"People don't want to buy their music as a subscription," Jobs told Rolling Stone magazine in 2003. "They bought 45's; then they bought LP's; then they bought cassettes; then they bought 8-tracks; then they bought CD's. They're going to want to buy downloads. People want to own their music. You don't want to rent your music -- and then, one day, if you stop paying, all your music goes away."

The enhanced Zune Pass is the latest in a series of moves by Microsoft in an effort to compete with the iPod. Earlier this week, Microsoft dropped the prices on its flash-based Zune players to levels below comparable Apple devices.

But Microsoft has introduced unusual Zune features before -- such as the ability to wirelessly swap tracks between devices -- without gaining any meaningful traction against the iPod. Apple's device has long maintained about 70 percent market share.

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