I used a cheap ESP8266 clone, a 5V relay and Blynk for a ultra easy hardware hack, that requires basicly no skills or programming knowledge. It should work for basicly all door buzzers, with a physical button to press. Touch can of course also be accommodated, but to keep this simple, i'll stick to the older "basic" phones. Normally when people are at my door, I have to get out of my chair, up from my bed, out of the shower- you name, and then walk to my hallway answer the buzzer and see who's at the door, and if they good people, buzz them in. I've now intercepted that button I press to buzz people in along with the contact it touches when I do, with each their wire and placed them in a 5V NO relay. Both the ESP and the relay are about a buck on most chinese sites, and are super easy to set up with the blynk service.Instructions (Translated from Danish)