In finishing up my new Windows Phone book, I had to deal with the confusing version problem. There are three version numbers to be aware of:

• Windows Phone 7.5
• Windows Phone OS 7.1
• Windows Phone SDK 7.1

So what is Mango? It comes down to this:

• Windows Phone 7.5: The marketing name of the phone. This is the phrase you’ll see in the ads to consumers.
• Windows Phone OS 7.1: The name of the actual operating system. When you create a new application in Visual Studio (or upgrade an existing one), you’ll see this version.
• Windows Phone SDK 7.1: The name of the Mango tools.

So get your nomenclature right and stop being confused.