Thanks to Chlettn over at Mobile-Review forums for pointing out a post on Telefon-Treff forums that reveals some information about an upcoming Eseries device that is supposedly called the E63.
The E63 is described as having:
-A 3.5mm headset jack on the top.
-Being thicker than the E71
-Having no front camera
-Bearing a mostly plastic body
-Packing a 2 MegaPixel camera
As you've probably gathered from these descriptions, the E63 is a cheaper version of the E71 - hence the E6x index.
Please remember that none of this has been officially confirmed by Nokia but Denver(a usually reliable insider on M-R forums )seems to have confirmed the above specs.
You can view the E63-1's User Agent Profile here.