Well it was so requested by Nokia E7 users to enjoy Symbian Belle on their devices like N8 users and C7 users have been doing. In fact E6 also has gained that Belle leak. Now here it is for Nokia E7.
A guy at IPmart-forum has posted a video with instructions to flash with phoenix.
Note: You can proceed with your own responsibility.
Phoenix Instructions
Belle Preview on E7
Update: Preview 2
Update: Preview 3
Video Previews by nadzyksieza
Download Firmware Files
Symbian Belle Firmware RM-626 http://www.mediafire.com/?iaf64uli59hlq9b
DISCLAIMER: We at techprolonged.com do not recommend flashing/refurbishing or manually installing official/unofficial/custom/hacked firmwares on your devices. You will be only responsible for any loss or damage to your device.
Note: We at techprolonged.com , haven’t tested this firmware. So we won’t guarantee it.
[source: ipmart-forum]