Microsoft today released Windows 10 Technical Preview for phones. If anyone bricked their device when tried to install this preview build, Microsoft has provided a way to get back to their prior OS. That is one of the reason, Microsoft didn’t release preview for large number of devices on the first day. They are supporting only phones for the preview that have a recovery image available. Microsoft has created a new tool called the Windows Phone Recovery Tool that will restore that image if necessary.
Download the new Windows Phone Recovery Tool here.