Windows 10 Technical Preview build is now available for the following Lumia Phone models and here is how to get it on your phone now.
1. Go to Windows Insider and click on the "Get started" button
2. Sign in with your Microsoft Outlook/Live account.
After signing in, you should be all set to get the Windows 10 Build on your Lumia phone, but only after doing the next few steps on your Lumia...
3. Download the Windows Insider app from the Windows Phone store on your Lumia.
4. Log in with your Microsoft Outlook/Live account
5. Click the "Get Preview Build", this should take you to the Enroll page where you have to select the Insider Fast option. This will search for the latest build and ask you to go to your Phone update to get download the Win10 build
6. Lastly, go to Settings>Phone update and update to the latest Windows 10 Build.