A few more tibits of interest:
Porygon2 is the only pre-generation V Pokémon to lack an animié voice, as it has never appeared in any episodes on the show beyond stock art. Porygon-Z, though never appearing in the show either, gained a voice through its (or for the Z in particular, his) appearance in Poképark Wii.
Porygon seems to become less restricted by its coding as a species in the Mystery Dungeon series as time passes. In the first games, Porygon would speak five preset sentences in a mechanical voice and little else, reflecting on the fact that it could not function beyond its programed perimeters.
In Explores of Time and Darkness, which presumably takes place after the events of Red/Blue rescue team, Porygon are able to speak on their own, a bit in a broken voice. They would pause between words and phrases, showing that they had difficulty communicating naturally, but their phrases seem to indicate that they feel happy towards the team leader and are eager to help the team's efforts in any way they can.
In the special episode on Explorers of Sky, taking place even further in the future, Grovyle and Dusknoir encounter two Porygon, presumably chased out of Temporal Tower quite some time ago. These Porygon are not only able to speak fluidly, but also show the ability to show emotions such as fear, something that was not indicated in their original programing and only added onto Porygon2 and beyond.
In the mystery Dungeon series, Alakazam has a lower base Special Attack then Kadabra.