I dismantled a push-button telephone and I am want to control it using a Raspberry Pi (A+) to trigger the button presses. The phone has a grid of 12 (+2 special buttons) contacts that correspond to the dial numbers. Normally the rubber domes would make connection when the button is pushed, but I want to find a way to close the circuit somehow using a Raspberry Pi. Below is a picture of the PCB. There's a potential difference of ~4.1 volts across the contacts.
I also need some way to close/open the latch that the handset would normally rest on, pictured below at SW2. It has the expected ~48 volts running through it, so it's waaaaay too much to directly control with a Pi. I plan on soldering a relay in there, as the contacts are easier to work with on the underside there. Unless there's a better way to do that.