Gamer News: DS in March outsold the 3DS.
Found here on Kotaku, the Nintendo DS outsold the Nintendo 3DS in the month of March. Sure, the DS had all of the MONTH of March to sell its units and the 3DS did have a smaller set of time to sell. The Nintendo DS sold at 460,000 units while the 3DS sold 400,000 units.
When it was released back in 2004, the DS sold sold 500,000 units in its first seven days here in the US, while the 3DS sold around 400,000 during its US launch. Smaller, yet most likely contributing to that number of 3DS sold was because of the launch title numbers for the 3DS compared to the DS's launch title numbers.
While these numbers make look like a bit of hit to Nintendo, the portable system will likely be more common as the DS when its software library picks up some more titles for everyone.