Now that the Flame device is available for purchase, the MDN site has been updated with specific instructions on how you can get Flame builds on the device. Please read through that page carefully as there are lots of tips that will help you flash successfully.
Make sure to first put a base image on the phone. The links below will lead you the directory for each of the branches we are currently testing:
Feel free to drop in #fxosqa on irc.mozilla.org and ask questions if you are having trouble flashing your Flame device.