You wouldn't know it from the publicity which mostly just mentions the fitness software, but the 5500 has a built-in step counter/pedometer so you can actually see how far you've run, walked or cycled.
I just thought I'd mention this because I've hardly ever seen any publicity blurbs emphasising this, yet it's the one feature that no other phone has (as far as I know), and pedometers are very popular at the moment with exactly the kind of keep-fit crowd the 5500 is aimed at.