I was considering between the 6510 and the 8310 and purchased the 6510 simply bcoz it was a newer phone with supposedly newer features.
Its true that the features are improved for a more executive style and resolution is definitely good compared to the 8310, but unfortunately the phone is not without problems of its own.
Opening and closing of message folders are extremely slow, probably bcoz the memory used is thru the phone and not the sim card anymore. But the gd thing is that you can now store 115 sms at least, not to mention the storage space in all the other folders.
The wallet function, which is new, also has lots of problems, somehow the phone hangs often just like a PC. And even though ive went to upgrade the software of the phone at nokia care centre, it does not seem to help at all. In fact it resets everything so all the effort of personalizing your 6510 is gone to waste.
The cover of the 6510 though isnt as attractive as the 8310, but the buttons are somehow easier to depress. And if you really like to change it to the 8310 express-on cover, u can do so with a little self-modification to the original 8310 cover and presto...u have yourself a 6510 inside an 8310 casing!
The bottom line is if ure a nokia fan then this isnt such a bad buy since frequent users of nokia phones are very much adapted to the user interface of the phone and that is really hard to change if you pruchase a new brand.