you need to catch a second Pokemon before you can trade, but since they're in the same region, yes you can.
trade them from Ruby, Emerald, or Sapphire, or... trade them from a friend, or... get them from the GTS.
You can do this after you find the Ruby and the Sapphire for Celio in Pokemon FireRed. then you can trade with Ruby, Sapphire and Emerald.
Pokemon Emerald: Birth Island Pokemon Sapphire: Trade from Pokemon FireRed, LeafGreen, or Emerald. Pokemon Ruby: Trade from Pokemon FireRed, LeafGreen, or Emerald.
You can't catch it on Sapphire. You have to trade it from Pokemon Emerald/FireRed/LeafGreen
Trade from Sapphire/Emerald.
You have to trade one from Emerald.
It Is Illegal!!
trade it from ruby or sapphire.
No, you have to trade from Ruby / Emerald.
You can trade with another sapphire, ruby, emerald, firered, leafgreen, Pokemon colosseum, Pokemon xd gale of darkness and Pokemon box ruby and sapphire.
Trade it from Pokemon Emerald/Ruby/Sapphire
only when you get the national dex on Sapphire version