Microsoft on Tuesday announced that the next version of its smartphone OS, Windows Phone, is now available and has begun shipping to customers around the world. Windows Phone 7.5 is a free update to existing customers and will appear on new hardware in the coming weeks, the company says.

"This morning, we began rolling out the Mango update to phones around the world," Microsoft's Eric Hautala wrote in a blog post announcing the release. "I'm sure you're as excited as we are: Windows Phone 7.5 (aka Mango) is our largest and most feature-packed software refresh to date."

According to Microsoft, over 98 percent of existing customers will be able to download and upgrade to Windows Phone 7.5 in the coming weeks, with only two carriers—T-Mobile in the United States and Telefonica in Spain—still testing the update. "This is a simultaneous, coordinated, global update that cuts across carriers, phone models, and countries," Hautala wrote. "This time, almost everybody is going first."

That said, it could be a few weeks before Windows Phone 7.5 is offered on your device. That's because Microsoft is metering the rollout to ensure that everything is working properly. So, today, 10 percent of customers will gain access to Windows Phone 7.5. That number will rise to 25 percent in a week, and then to 100 percent two weeks after that, assuming everything goes well.

Windows Phone 7.5 is a big and important update to Windows Phone. That being so, I have a ton of content ready to share with you on the SuperSite for Windows, and more is coming soon. Today, I have the first two parts of my four-part Windows Phone 7.5 review available, an extensive screenshot gallery with more than 100 screen captures, and, later today, an editorial that explains why this release is so important. Tomorrow, I'll wrap things up with the final two parts of my review.

So stick around, folks. It's going to be a wild ride.