Microsoft has released Windows 10 Mobile preview build 14342 for members of the Windows Insider program in the Fast Ring. If you're in the Insider program, you should be able to start pulling the the update down to your Windows Phone now.
With this update, three new devices are now eligible to receive updates from the development branch. From Microsoft:
We are excited to announce that we have added 3 new devices to the list of devices capable of receiving updates from our Development Branch as part of the Windows Insider Program: Lumia Icon, BLU Win HD LTE 150e, and BLU Win JR 130e.
Do be aware that, due to a bug, you will see this update show up as build number 10.0.0.1001 instead of 10.0.14342.1001 in the "Phone update" portion of the Settings app.