What do you mean not illegally? Getting bandwidth that you're not paying for is called stealing and stealing is ILLEGAL. Also the phone company has to hook up a DSL circuit to you phone line to make it possible to use. So it isn't possible to just hook up a DSL modem to your phone line and get DSL bandwidth. If you want DSL you're going to have to pay for it.
Here are some DSL providers: Verison SBC Earthlink