It’s important to keep in mind you’ll need to have collected at least 60 Pokémon and completed the Sevii Islands sidequest to open up trading.
Ask a friend to borrow his Game Boy Advance; this will save you having to purchase another console in order to make the trade.
Don’t forget to use the Master Code (00006FA7000A 1006AF880007) if you’re having any troubles with the code being accepted. [2] X Research source