The Nintendo DS and DS lite does not have a friend code system so there is no way to get friends on Pictochat. As long as your friend is within range of your DS console, you can communicate through Pictochat but you cannot save friend codes.
pictochat is where if u have a Nintendo ds it can talk to another ds within a certain range. you use the touch screen to write or draw things. it also has info about picto chat in the manual that came with it
Yes, since both the Nintendo DS and DSi has the Pictochat application, you can connect these two systems together. However, the Nintendo 3DS does not have pictochat, so the 3DS will not be able to connect