Voice signals and DSL data signals are carried to a given user on the same segment of copper wire. This is possible because the voice and data signals are carried over different frequencies. This works very well on paper, but in real world applications, when both phone and data signals are coming to a user simultaneously, there is some moderate interference. A DSL filter works by minimizing this interference, making for a faster DSL connection.
I do not think that you can; I hear that SLT automatically disconnects your connection after 10 hours(I am assuming you are using an slt connection)I had a similar problem before so I had to buy a router.