Microsoft is now offering a download of Windows Phone 8.1 early. There is a catch though; you have to be registered as a developer to get the download early. You can also be running a smartphone that is "developer unlocked" to get the update. Microsoft said that this preview period is aimed at allowing developers to be sure that their apps will run correctly on a phone before the update launches to the general public.
If you don’t have a smartphone that is "developer unlocked" you can register as a Windows Phone developer for $19 allowing you to publish apps to the Store. Users can also register as a developer with App Studio, which is free and lets you create apps that run on your own Windows Phones. If you want to "developer unlock" your smartphone, you can download the developers tools and register that way.
There are some catches to this free preview update that you need to be aware of. Installing the preview update could void your warranty according to Microsoft. Microsoft's preview is only available with the Microsoft portion of the update. Mobile operator and OEM driver updates won’t be offered until the official update for the user's phone is available.
The biggest catch to applying this preview update is that you can't revert to a prior version of the operating system. That means if you apply the preview and it doesn’t work well with your device, you are stuck. Microsoft says that those who install the preview update will be moved forward to release state when available. check out our hands on with Windows Phone 8.1 for more details.