DSL uses the same two lines as the phone. No one mentioned a splitter or filters.

Have Verizon install one for you OUTSIDE in the NID. There new ones are really cool in terms of what you can do testing wise.

The NID typically presents a 1/2 ringer load.

The splitter basically brakes up the DC and ring signals and passes the voice band which includes about 3 Khz. Frequencies up to about 5 MHz are used by the DSL modem in bands.

I have the worst interior lines in terms of number of phones, locations, bells and non-home run, Mostly quad wire. The Telco guy says the DSL is pristine though. The original splitter I installed in the NID. When the NID was installed a length of 4-pair was run inside the house.

The highest pair, I reserved for DSL. The DSL section is about 3" to a punch down block and then to a CAT3 RJ11. I run CAT4 RJ11 direct to the modem about 5 feet away. The DSL line can be polarity reversed, so I use a straight thru Cat4 RJ11 cable.

Telco is a hodge-podge mess mostly installed by the phone company in the 60's. There are basically two origin points and some piggy backing off of existing jacks.

I'm planning a switch at the DSL modem that will do modem #1, modem #2, Reverse, normal. but I haven't rewired the switch to CAT5.

So, telco goes to a carbon surge protector/studs on the inside, which I could pull the carbon out because surge suppression is also done in the NID.

For now, it works, but a few internal lines have been disconnected. Spiders and water. I did make a few quad wire to CAT4 spice boxes. The first one is not quite in service yet, A non-removable terminal strip for the quad wire and a removable strip for the CAT4 so I can easily disconnect the one that likes to get water in it. I'm in the process of installing a CAT6 patch panel for network and phone. It's currently vacant right now,

Anyway back to DSL. If the Modem is connected and powered on to the DSL line without a filter or splitter you will hear a high frequency hiss in any phone without a filter, Turn off the modem and the hiss goes away. Picking up a phone could cause modem issues if turned on.

The phone will work if the DSL modem is off and the modem will work as long as no phone is picked up if there is no splitter or filter.

Filters are limited to 4 or 5, I think 4. You only need a single splitter and the DSL quality goes up.