Blueds
Pokemonfan18 has an article on use the DS over a dial up connection – “This tutorial is to help you get connected to Nintendo Wifi with a dial-up connection. Even though lots of people think that wifi with dial-up would lag and cause the people with high speed internet to go slow, that is not true. At normal dial-up speed (56kb) it will go just about as fast as high speed internet..” Link.