This is unfair comparison because I use the III for years and the Pixi
for hours. I also compare a real PDA with a phone.
PIM:
The older ones are more elaborated and much easier to use. They also
have more features. The only plus (for some) for the Pixi is an on-line
sync with the Google calendar (in theory as Google APIs changed over
time and now I have had no success in connection to my Google account
from the WebOS.
Reading:
No Plucker on the Pixi. There is an app to read some PDB and ePub
files, though. I have to test it.
Calculator:
Nothing at least partially comparable with the EasyCalc on the Pixi.
Gaming
The DopeWars are available on both devices. Wow!