There are several ways to filter your telephone line so that the DSL signal doesn't bleed into your voice communications. One way is by using individual filters on each telephone jack in your house, however this has been known to cause confusion and over time having the filters removed for some reason or another causing the DSL to stop functioning. You could also have the telephone company filter your entire house for you, but that costs about $100 and the in-line filters they use tend to blow out in electriclal storms which may cause you to even loose your dial-tone.
     The procedure outlined here is for people who have a SNI (System Network Interface) at their house, have only one phone line, and have their SNI and house pre-wired to support two lines. This is NOT for the timid. If you don't know what you're doing then don't even try this. If you break something, then don't blame me. It works for me and it works for everyone else I've talked with that has tried, but that's not to say that it will work for you.
     Most of the newer homes (<20 years old) are already wired for at least two phone lines regardless of how many you need. In doing this they make the 2nd line pair available for anything you want. We are going to take full advantage of this.
     The SNI (also known is a "NID") is normally located near the electric meter or by your house's ground spike and is grey or beige and about 6"x6". There are normally 2 ways to open it. The telephone company side is opened with a hex wrench, but you don't need to worry with that. The other is opened with a regular flat tip or philips screwdriver (the customer side).

     Once you open the customer access door there should be two telephone jacks with cords plugged in. The jacks are where your telephone service is provided and the cords are what supply the signal to your house. Most of the time the telephone company is nice enough to label the lines with their appropriate telephone number, however if they are not, as in this example, you will need to bring a cordless phone out there with you. With cordless in hand check for dial-tone, then unplug one of the cords. If you lost the dial-tone on the cordless then that's the line that's going to be filtered, if not then try the next one.

     Unplug the cord that has your dial-tone on it and plug in the filter in it's place, then plug the cord into the jack on the filter labled PHONE. The other line (optional line 2 cord) needs to be plugged into the jack on the filter labled DSL. This will activate the line 2 pair on every jack for your DSL modem and filter the line 1 pair for all of your phones in one fell swoop. There should be enough room to tuck the filter up in the box nice and neat, then you just need to screw the lid back down.

     If you look at a telephone jack in your house you'll notice that it has 4 copper contacts in it. In most cases only the center 2 are used (the line 1 pair), however now that we have the DSL split at the SNI you'll need to connect the DSL modem to the ouside 2 wires (the line 2 pair).
     NOTE: Do NOT use a 2 line phone with this setup unless you use a telephone cord with only 2 wires.

     In order to do this you need a 2 line splitter (couple of bucks and a trip to Radio Shack). It will take the 2 line jack and split line 1 and line 2 into two separate jacks. Just label the line 2 jack with a Sharpie so you can see which one the DSL goes into when you're under the desk. The jack labled "L1+L2" should only be used for a regular telephone, since all this is is a copy of the wall jack it's plugged into.