NVIDIA's GT300 Fermi might support GDDR3
 

There is a chance that some of the GT300-based Fermi devices might end up with GDDR3 support. The memory controller is 384-bit wide in Fermi “GTX” single chip 512 shader version, but in some less expensive chips they will use less memory bandwidth and even GDDR3.

We believe that in entry level, at least in some SKUs GDDR3 makes sense due to its lower price, as GDDR5 is still quite expensive. Fermi is a very scalable architecture and since the high end chip has 16 clusters and entry lever ones could end up only with a few clusters, that will make them small but still powerful enough for the desired market.
http://www.fudzilla.com/content/view/15833/34/