Microsoft on Monday announced a major new update for Windows Phone 8. And while the free update will improve existing phones, the biggest changes enable a new generation of so-called "phablet" devices with 5"-to-6" displays and 1080p "Full HD" resolution. The best news? Any Windows Phone 8 user who wants the update early will be able to get it this week.

"Windows Phone 8 Update 3 will roll out to existing phones over the next several months," Microsoft's Darren Laybourn notes in a new post to the Windows Phone Blog. "We're seeing things really start to accelerate ... because we continue to advance the platform at a rapid pace. Our hardware partners, meanwhile, have been taking advantage of this innovation by releasing amazing new Windows Phone devices throughout the year."

Windows Phone 8 has seen great success this year at the low end of the market (Laybourn cites the platform's 10 percent market share in Europe, which is due in large part to the $99, no-contract Nokia Lumia 520), but Update 3 aims for a new part of the market. Dubbed General Distribution Release (GDR) 3 internally, Update 3 positions Windows Phone for "phablets," the fastest-growing smartphone segment.

To this end, Update 3 adds support for larger, 5"-to-6" screens that can support Full HD 1080p resolution. It also supports a more powerful quad-core processor, the Qualcomm Snapdragon 800, where today's Windows Phone handsets top out with dual-core processors. There's a lot more, but you can read about the full Update 3 feature set in my "Windows Phone 8 Update 3 Preview."

The arrival of Update 3 corresponds with two additional releases.

First, Nokia will be announcing some new devices next week that will ship with Update 3 and in fact require certain Update 3 features, including that big screen and Full HD resolution support. These devices will be announced at a special event in Abu Dhabi on October 22. Other phone makers are expected to announce Update 3-capable devices soon, as well.

Second, although existing phones will get the update over the next several months, Microsoft has finally figured out a way to work around carrier restrictions and deliver Update 3 to end users who want to get it early. Starting tomorrow, on Tuesday, anyone who wants Update 3 can get it via one of Microsoft's developer programs. And one of them, called App Studio, is free: Just register at the site and you'll be able to download a new Windows Phone Preview for Developers app that will enable you to download and install Update 3 directly on your phone, over the air. (Later, when Update 3 ships on your carrier, you can get the handset maker and carrier firmware updates and drivers that would normally accompany the public release.)

These are important changes, and I'll be writing a lot more about Update 3 in the days ahead. Stay tuned to the SuperSite for Windows for more information.