An excerpt from the IGNPocket article:
Sonic the Hedgehog, or Sonic N, is just a scaled down version of Sonic Advance. The levels are pretty much exactly what GBA owners can already play. What’s more, the Nokia version is severely letterboxed, squashed, and distorted when it’s fit on the vertical LCD screen, making the text and score very, very hard to read. The game’s speed is equal, but the refresh is not…and this limitation is noticeable when Sonic blazes at top speed, and the screen’s refresh makes the scrolling look a bit choppy.
Source: IGNPocket