Microsoft unveiled Windows Phone 8 today, its next-generation smartphone operating system. But what exactly does that entail, when can we expect to see devices, and what does it mean for people who have Windows phones now?

What are hardware changes?
Near-Field Communication (NFC), support for multicore processors (like dual-core and quad-core), new screen resolutions (like 1,280×720-pixel HD), and expandable memory slots are the biggest news in terms of hardware changes.

What’s with the new start screen?
Microsoft’s redesigned start screen (pictured above) spans the width of the screen now. You’ll be able to resize each individual live tile from the start screen to one of three sizes. There’s also support for new color themes, which Microsoft didn’t list.

What else is new?
There’s also support for in-app purchases, and a “wallet” for storing sensitive account information and loyalty cards, to name a few. Phones get over-the-air OS updates, instead of tethering to the desktop to update. Windows Phone 8′s architecture heavily overlaps with Windows 8 for the desktop and tablet, so there will be a great deal of similarity in the way that the OSes handle security, gaming, networking, media playback, and so forth.

Read here for more details about what’s new in Windows Phone 8.

When can I get it on my Windows phone?
New Windows phones running WP8 will ship in the fall. Microsoft also used the term “holiday season,” which could really mean anywhere from late September all the way to just before Christmas.

Bad news for existing Windows Phone owners, though. There’s no upgrade path from Windows Phone 7.5 handsets to the forthcoming OS. We know, we feel your pain. You just bought your Samsung or Lumia phone and it’s already obsolete. Now before you get your knickers in a bunch, consider this: it’s mostly a hardware foundation that’s going to make Windows phones far more competitive going forward.

Well, what can I get, then?
Microsoft threw you a bone. A small bone, but one that Redmond hopes you’ll find tasty nonetheless. Windows Phone 7.8 is an update that will give current 7.5 Mango users the new start screen to play with. Microsoft did not announce an update schedule to Windows Phone 7.8.

What does Nokia say?
Nokia is also offering several apps on its phones: Play To content sharing over DLNA, Nokia Maps with commuting intelligence, Nokia Music 3.0 with Mix Radio, Nokia Drive, and camera extras, which include panorama, burst shot, and GroupShot (it’ll find photos with the nicest smiles and open eyes.) Camera Extras and Counters will come to the U.S. and China by June 22, and to other countries in July.

Zynga games like Words with Friends and Draw Something will be available to Lumia owners for the next couple of months, Nokia said. There’s also a usage app to monitor texts and calls.

When do developers get the SDK?
Microsoft will go into deeper details with developers later this summer, which is when they’ll also get the SDK.

Who’s making the phones?
Samsung, Nokia, HTC, Huawei, and ZTE are Microsoft’s five largest partners, but we’ll see Windows phones from other manufacturers as well. Samsung and Nokia have already shown a range of higher-end and more midrange Windows 7.5 handsets here in the U.S., and Huawei and ZTE have demoed the more affordable, entry-level Windows Phone handsets globally. We expect the trend to continue with Windows Phone 8.