Blogger Mike Zornek has hit the nail on the head when it comes to friend codes and upgrading to the DS Lite once
it hits a local retailer near you. Since your Wi-Fi ID is dependant upon the combination of hardware and cartridge,
popping in Mario Kart or Animal Crossing: Wild World for some WiFi action
only allow you to connect to your existing list of friends after some tweaking and transferral between your original DS
and the new one.
Thankfully we all have wonderful sites like DS-Play to help make the transition easier.
[Update 1: Oops! We totally forgot that you can transfer your Wi-Fi ID to your new DS via the Wi-Fi settings menu. Just don't sell your old DS before doing so! Thanks to our invaluable readers for rightly reprimanding us!]