The company has been trying to move away from the old Skype username system for a while now, but until today Windows Phone 8 owners had a choice of using their Skype or Microsoft Account login. In a blog post today, the Skype team says that new Windows Phone users can simply access the Skype app with the same Microsoft Account info they registered when they got their device. Current phone owners who have used their Skype login before today will now be prompted to sign into the app with their Microsoft Account email address and password first before typing in their old Skype name and password; this one time step will link both accounts together.
Starting today, all Windows Phone users signing up to Skype for the first time on their Windows Phone will register with their Microsoft account. This is the email and password you entered when you first set up your Windows Phone – the same account you use for other Microsoft services like OneDrive and Outlook.com. Once you've set up your Microsoft account, you'll use it to sign in to Skype on all your other devices too. Get more detailed instructions here.