Microsoft today will detail the features coming in its third major update to Windows Phone 8, now called Update 3 but previously known by the internal moniker GDR3. Update 3 will be made available for free to existing handsets over the next several months, as you might expect. But the good news is that the firm will also allow developers--really, anyone--early access to Update 3 starting tomorrow.

So why now? Update 3 will of course be included on new handsets, starting with some exciting new models that Nokia will announce next week. So this feature set serves as a general preview, if you will, of some of the new features we can expect on those devices.

Mile-high view

Update 3 is an important step for a platform—Windows Phone 8—that was designed to have a not-so-speedy 18 active month life cycle. It increases the build number of the OS to 8.0.10512.

According to Microsoft, Update 3 had three main engineering goals: Enable a new generation of incredible Windows Phone 8 devices, enhance the platform with new capabilities for current users and partners, and improve overall quality.

Major new features

Update 3 delivers the following improvements to Windows Phone 8.

Bigger screens. Update 3 allows Windows Phone 8 to be used on screens of 5- to 6-inches, enabling so-called "phablet" handsets.

1080p. Update 3 also allows hardware makers to deliver devices with 1920 x 1080 (1080p) screens. Such a screen provides room for room for six small-sized live tiles horizontally instead of four, as is the case with today's screens. Built-in apps and hubs like Mail, Photos, People, and Music & Videos will also be "carefully scaled" to take full advantage of the additional on-screen real estate.

Quad-core processors. While today's Windows Phone 8 handsets are limited to dual-core processors, Update 3 will add support for the Qualcomm 8974 quad-core processor.

Driving Mode. A new feature called Driving Mode works with a connected Bluetooth device to limit notifications on the lock screen—including texts, calls, and quick status alerts, Microsoft says—until you're safely parked. You can configure Driving Mode to send automatic replies to people who call or text while you're driving.

Mobile Accessibility. One of the big complaints about Windows Phone is that its accessibility features are decidedly lacking. With Update 3, Windows Phone 8 picks up a suite of apps called Mobile Accessibility that seek to improve this situation. Apps include a screen reader for blind and visually impaired as well as tools for the hearing-impaired that help with notifications like alarms, calendar events, and low-battery warnings.

Tethering improvements. The Internet Sharing feature in Windows Phone 8 is being updated to include a special pairing mode for use with particular PCs that uses Bluetooth to make the connection: No more manual entry of passwords.

Better ringtones. With Update 3, you can use custom ringtones for more events, including instant messages, emails, voicemails, and reminders. You can also configure custom ringtones for contacts for text messages. (Previously, you could only do so for phone calls.)

Screen rotate lock. Yep, you can now lock the screen rotation, just like a real smart device.

Improved storage management. While GDR2 added the ability to automatically manage "other" storage in the Phone Storage settings app, Update 3 now provides a new category view that shows exactly what apps and other items are using up that space.

Manually close an app. Now when you access the App Switcher multitasking screen (by pressing and holding on the Back button), you will be able to manually close an app using a large and obvious close ("X") button.

Wi-Fi access during Setup. In the current version of Windows Phone 8, you cannot connect to a Wi-Fi network during Setup, so you must have a cellular data connection to add a Microsoft account. With Update 3, Wi-Fi configuration occurs before this step, solving a major complaint, especially for those of us buying no-contract phones like the Lumia 520 where a cellular connection is not guaranteed.

How you can get Update 3 this week

OK, so Update 3 is obviously a big deal, and everyone is excited that new handset users will get it soon. But what about existing Windows Phone 8 users?

As before, you can simply wait to get Update 3. Microsoft will offer it to wireless carriers for testing and delivery as before, and most will cause us to wait months and months before we can actually access the update.

Or.

Microsoft is also announcing a new Windows Phone Preview Program for Developers, which it says is designed to give developers—cough—early access to upcoming releases so that they can test their apps before release. This is exactly what Apple does with its own iOS developer program, which costs $99 per year. Indeed, this summer, I downloaded 7 Beta releases of iOS 7 between its June announcement and the October release.

Microsoft's Windows Phone developer program, however, is just $19. Which is quite a bargain. But you don't actually need a full $19 dev program membership. To qualify for the Windows Phone Preview Program for Developers, you can also use an App Studio account—which is free—or simply be lucky enough to otherwise own a developer-unlocked phone. (This typically requires a Windows Phone developer program membership.)

So if you don't feel like spending $19, head on over to App Studio and register.

Here's how it will work.

Visit the Windows Phone Preview for Developers web site (this will become live later today) and accept the terms and conditions. Then, download the Windows Phone Preview for Developers app, which installs from the Windows Phone Store directly onto your phone over the air. This app lets you opt-in new updates directly from your phone. Then, simply visit Phone Update in Settings and check for updates. Voila!

Microsoft notes that the version of Update 3 you download this way will only include Microsoft's code, and not the handset maker and carrier firmware, driver and other software updates that will be added to the public release. And when you participate in this program, you can only move forward with regards to updates: There's no going back. Furthermore, it's possible this update will void your wireless carrier warranty.

Given the history of Windows Phone, I suspect few will care about any of this.

Information for developers

For actual developers, Microsoft will provide Update 3 emulator images for Visual Studio in the next three weeks. But there are no new APIs in the update, so there will not be a corresponding SDK release. Truth is, there really isn't much that you need to do to get your app ready for Update 3. Which, of course, is what makes the release of the Windows Phone Preview Program for Developers so delicious.

That said, there are a few things to be aware of. The background audio memory cap increases from 20 MB to 25 MB for phones with 1 GB of memory or more, for example. The Internet Explorer and WebBrowser control viewport has changed because of the new resolution support. And of course with 1080p resolutions supported, you may wish to provide higher-resolution graphical assets in your apps.

So there you have it. Good news all around. What a welcome change.