After working with computers since we knocked holes in the cards in 1973 I cannot think of any reason technically how a door buzzer would impact a DSL ... Wireless connection maybe some interference but that is blowing smoke at you Art.

That is like saying you can't start your car because there is a tree root growing under the driveway ...

I would get a cable modem, you don't need to buy the cable TV programming. I just ditched mine for a dish but I still use the internet service. In my area the DSL is the same price but the cable is far faster. I would just tell them you want the internet service and nothing else