This is all good, but now we hear from our sources that “Preview for developers” will not come on 8th or 10th, but on or around 14th of April, a date on which it will actually hit gold and will be seeded to manufacturers as well. The blog post by Joe Belfiore on Windows Phone 8.1 features also mentions first part of April as the time-frame for Preview for developers availability.
Windows Phone 8.1 will start rolling out to existing Windows Phone 8 users and will come pre-installed on new phones, including the Lumia 630 and 635 and Lumia 930 announced by Nokia today, in the coming months. If you want to try out Windows Phone 8.1 and you are a registered developer, you can update your phone as part of the Developer Preview Program in the first part of April.
If you remember preview for developers app lets you update your device to latest OS version from Microsoft and if you have a app studio account it becomes a free update.