The recently announced Lumia 510 looks a lot like the Lumia 710, from it's design, the back cover to look and feel of both phones, but make no mistake there are not the same.
So I put together a nice comparison table to show the difference between the devices...
As you can see, the Lumia 510 is really really low end, in fact the only thing going for it is its 4inch display, then it's all low specs from there.
Even the low end Lumia 610 has higher specs than the 510, with an internal storage of 8GB (510 has 4GB) but the 610 still has a 3.7inch display. apart from that, both phones have everything the same.