If you are wondering on how to Evolve a Pokémon that requires Trading and/or with an Item and only have one DS/DSi/DSi XL, well you can use the GTS (Global Trade Station) Glitch.
For HG/SS users, the GTS (Global Trade Station) is located West in Goldenrod City. For D/P/PL users, the GTS (Global Trade Station) is located in Jubiliy City.
DIRECTIONS
• 1st, Deposit the Pokémon you want to Evolve.
• 2nd, choose a Lv.100 Abra in return.
• 3rd, Search for any Pokémon that you can Trade with.
• 4th, Trade with that Pokémon.
• 5th, go back and Withdraw the Pokémon that you had Deposit.
• 6th, the Pokémon will now start to Evolve.
• 7th, the Game will now automatically Save.