You have 40mb free on the 8100?? Wow! You must have starved that thing to death! I run lean and only have 25MB! But I do have around 10k messages on the device (I know, I know...it's just nice having history at your finger-tips!
I don' think you will see that range on the Curve as the higher end of free space I am hearing is like 21mb your 24mb is the highest I have heard.