It may be small but the first change is the logo on the top right hand corner. At least it'll be easier to quickly identify the latest version without having to go the 'About the S8602' screen. The second main change can be found in the advanced audio settings which now have three dropdown boxes. It's here that you set up the softphone to use a headset but to send the ringing to the pc speakers.
I've had a look around the other setup screens (which to be honest are minimal) and I cannot find any other visible changes for the user so in summary the user changes can be categorised as follows:
Softphone now works on Vista
Ringing can now be set to go to PC speakers rather than headset