The new ho-hum iTunes phone from Motorola, the ROCKR, is crippled by pointless, restrictive DRM that stops you from loading more than 100 songs on it, no matter whether they fill your storage:
The phone includes a removable 512MB Flash memory chip (found under the battery in the back of the phone). This chip will hold up to 100 tracks but the number of songs it holds isn't dependant strictly on the size of the chip (though it obviously can't contain more than 512MB of data). Rather, the 100 track limitation is part of a DRM scheme that prevents the phone from playing more than 100 tracks.
iTunes 5 keeps track of the number of tracks authorized for playback on the phone so even if your 100 tracks have used only 350MB of the card's capacity, you can't add more. Similarly, although you can swap in a new card that contains new tracks, those tracks won't play until they've been approved for playback by iTunes.
