Microsoft is keeping new features and improvements for Window 10 for Phones limited to those who own one of the six smartphones compatible with the technical preview of the new operating system.

However, the next build of Windows 10 for Phones may expand compatibility to additional smartphones. Although Microsoft hasn't yet announced which smartphones will be added to the growing list of supported devices for Windows 10 for Phones Technical Preview, it did confirm the information.

Now we don't know exactly when the next version of Windows 10 for Phones will be released, but we can guess it will be pretty soon because some screenshots have just leaked online.

The new build version 12521 isn't available to everyone yet, but some screenshots have been published on the Polish forum Windowsmania.

Along with these screenshots, there are some details pointing to some of the new features Microsoft will include in this build.

Some features will only be available on certain Lumia phones

One of the most important would be fact that users will be able to set LED notifications for the smartphones. However, this feature will only be available to those who own a smartphone that has a hardware LED integrated like the Lumia 730, Lumia 735 and Lumia 930.

Once the new version of Windows 10 for Phones hits some of these smartphones, the LED hardware should become active and allow users to receive notifications.

There's also a new option that will allow users to remove their Microsoft account without having to factory reset the smartphone.

You can now also sync settings for the apps you want or web browser, theme and passwords. There's also a new Microphone settings menu where you can choose which apps installed on the phone can use the microphone.

According to the source, these screenshots have been taken from a smartphone with access to Windows 10 for Phone Technical Preview test builds, so the OTA (over the air) update hasn't been released yet.

Take a look at the screenshots in the gallery and tell us what other new features and tweaks you have noticed.