Yeah, you can do it actually. Via Nintendo Wi-Fi connection however. You can't do it via the normal Wireless Communications without two DS'.
If you don't have two DS Handhelds, you can establish a link over Wi-Fi. Remember, you need WEP Encryption or no Encryption when using Nintendo Wi Fi. That being said, DSi and 3DS users can set up "advanced" connections for WPA2 Encryption.
Register the first Pokemon Black or White at the Pokemon Global Link. To do so, you'll need to use the Game Sync feature at the Main Menu of the first Pokemon Black or White. Use the Game Sync ID to register the game at Pokemon Global Link after creating an account.
Next, insert Pokemon Black 2 or White 2 into the DS. Start up the game and select the Memory Link option from the Unova Link menu at the start menu. Select the Wi-Fi option and enter the same Game Sync ID. A message will pop up confirming the link.
Source: IGN's page on Memory Link