Many of the terminals in the phones I might use have connectors designed to attach to screw terminals. This makes it a little difficult to attach to a standard Arduino. Here is my way to adapt them.
Start with a 3-inch wire that has been stripped about half way.
Position the wire so that the stripped portion is near the base of the lug.
Wrap the wire around the back of the lug, through the center of the spade, and back around to the other side.
Cover with shrink tubing to hold the wire secure.
After all that, you can strip the end of the exposed wire, and use it with a regular Arduino, or as I did, with a Boarduino.
The two grey wires with white shrink wrap are from the dial mechanism and connect D2 to ground (chosen to get pin interrupt 0), and the other two come from the hook switch, and connect D7 to ground when "on-the-hook".
In retrospect, it probably would have been a good idea to take some sandpaper to the connectors to remove some of the oxidation. However, these won’t be carrying high currents, so the connections are good enough.