These blocks are often found in basements and can still be in use, but never in newer homes. Most newer homes have two plastic boxes outside with wires coming out of them. One for the cable TV wiring and the other for the incoming phone line.
The phone “box“ is called a telephone interface which is the modern version of the connector in the photo. The block is where a repair man could attach a handheld telephone to the terminals with alligator clips to check the incoming phone line for faults and determine if a fault with the house phone was in the house wiring or out at the street.