yes, a nintendo event-with the wireless adapter thingies
you need 2 wireless adapters for the GBA/SP
2 games that's FR/LG/E
both of the games you use have to have gone into a pokemart and filled the questionare "link together with all" and the owner of the shop will say bla bla bla,,,, then turn the power off then put the wireless adapter on and plug it in where you'd plug a link cable in for trading, (both games do everything i say btw) and then turn your GBA/SP on, turn pokemon on, but don't load your saved file, instead there will be a new selection called "mystery gift" so press that one, and i dont know if you press cards/news, but press one of the 2, if the one you choose doesnt have a selection called "wonder gift" then its the other. then press on the "wonder gift" and let it rest, but don't turn your GBA/SP off, and set the 2 GBA/SPs together, make sure that their wireless adapters are facing eachother, and after a while, it should work, and once you talk to the ship guy who would takeyou to the islands, press "birth island" when it shows the list of the islands when you talk to him. then he will take you to 9 island, that is wehere you get deoxys.
i do NOT know gift you have to do to go to rainbow island, you do the same thing to get deoxys, but in the mystery gift bit, i forget what gift it is you have to press on, sotry them all, its ONE of them ^^