Hi, I have already played once Pokemon saphire, and now I play Pokemon soulsilver version. But, when I played on Saphire, I had a Kadabra but he doesn't evolve. My question is how does the evolution by trade works?
You trade the Pokemon via Link Cable or Wireless Adaptor to another Gen III game (FireRed, LeafGreen, Sapphire, Ruby, Emerald). After your Pokemon, in this case, Kadabra, gets into the other player's game, it will start evolving.
That's all, really.
Just trade it to a friend or yourself(if you have another DS and Gen 4 game), then the Kadabra will evolve. Trade it back to your game and you will have a Alakazam.
Trading certain Pokemon such as alakazam can trigger an evolution in them. In the Gen I -III. U would need a special cable to do so. With IV gen you could trade wirelessly. This can be a frustrating way to evolve Pokemon, but Im guessing it was only made to encourage co -op play.Some Pokemon like syther and seadra need an item to evolve as well.