If you’re the user of a Windows Phone device then we have some important news for you today as yesterday some changes were made to the Marketplace for apps. This means that your phone will need to be running Windows Phone 7.5 from now on to access the Marketplace so that if your device is using an earlier OS version you’ll be unable to download, purchase or review apps.

Many of you with Windows Phone devices will already be running WP 7.5 that arrived last fall and so you won’t notice any changes at all. Nevertheless there may be some users who will still be running earlier software and may be slightly baffled that when they try to access the Marketplace they will come across an error message if they try to download a new app, or also update an existing app.

The changes apply to the phone and also the web Marketplace storefronts and will be implemented over the next couple of days so even if you don’t hit problems now, you soon will if your device is not running WP7.5. It’s simple to update to Windows Phone 7.5 if you need to, so if necessary you can check out how to prepare for the update and see step-by-step instructions here. You’ll need to connect your phone to your computer with a USB cable and then simply follow the Zune software or Windows Phone 7 Connector for Mac directions.

As the Windows Phone Blog points out, even if you don’t use apps and don’t visit the Marketplace the update to the Windows Phone 7.5 OS has plenty of advantages with hundreds of improvements made. If you want some idea of the enhancements then check out this page that shows what’s new in WP7.5. If you’re not sure what OS your device is currently running then head to Start and flick left to the App list. Then tap on Settings >About> More Info to find out.

Have you found the error message when trying to access the Marketplace? If you install the Windows Phone 7.5 update let us know if all goes smoothly and if you can now use the Marketplace again by sending your comments.