oh, yea it uses a pretty old version of it, Symbian 6.1 with S60 1st Edition.
About until the 3rd edition, the first and the second edition remained the same in design. Early phones in the N-series had a more skeuomorphic UI design, which then got to other Nokia phones, including non-Symbian ones. Then in 2009 they switched to the flat design, which i unofficially dub "the Ovi design"