Today, Microsoft announced not only the Windows Phone App Studio tool but also some updates regarding the Windows Phone development platform. Starting today, any non-developer account can unlock one phone for free and load up to two apps; registered Dev Center developer accounts (i.e., accounts with an annual fee of $99) can still unlock up to three phones, each with up to 10 apps. Unlocking and deploying XAP files will still require the Windows Phone SDK.
If you wish to publish your app to the Windows Phone Store, you will still need a Dev Center developer account. As Microsoft announced at Build 2013, developers can still register for a developer account for $19 before August 27th (registration link).
The Windows Phone Dev Center now offers a "Click to Chat" customer service option. In this update, payment support for the Windows Phone development platform has been expanded to include six additional markets, bringing the total number of supported markets to 128. This means that developers in these six new markets can now release paid apps.
Microsoft also announced the latest figures for the Windows Phone app ecosystem: it has now reached 2 billion app downloads, with the most recent 1 billion downloads taking just six months. (via Windows Phone)