iPods have long had some very limited data entry. You can modify ratings and build 'on-the-fly' playlists. I think that's about it.
The new iPods, however, have the ability to the ability to enter a string. Lower case and numbers only, used to search for songs. The data entry is rather slow, but since it auto-completes against a small string set it's probably quite practical. Hard to imagine entering phone numbers or addresses this way however.