Hey Gettinold! You may need your new big old fat buddy from Indiana after all!
Since you posted the hot pics, I'll help you with your situation. Everyone has given good advice but here is some with a step by step solution.
1. Have your brother in law calm down, this is not the end of the world!
2. Oustside you house is a telephone company interface box. One side opens for customer access. In older homes, the installers ran one four conductor wire from the outside and just looped through every location where inside jacks were needed. Take a regular wired phone with you outside, open the customer access side. Inside you will see the house wires under red and green screws. a short flat wire with a RJ-45 plug connects the customer wires to the phone company side.
Unplug the short modular plug and plug your regular phone in and see if you get a dial tone. You mentioned that you are using DSL so you should have the newer box as I am describing. You should have a DSL filter on each inside line that is only used for phone.
3. To answer your other questons, old phones used two wires the same as the newer ones, usually red and green for the phone. The yellow and black was commonly used to connect to a low voltage transformer block to power the lighted phone dials. If not used for this, they could be used as an alternate pair for phone signal or for a second phone line. Since the red and green seem to be terminated, the yellow and black are your signal wires. The pic you posted looks like it has six screw terminals which will Carry up to three phone lines but you most likely use only one of these pairs. The reason I describe the other combinations is that just wiring the jack wrong and not having a phone plugged in should not disrupt service to the other jacks in the house. The exception to this is if you would have one of the old transformers feeding 6 volts AC to your wires.
So, first verify that the line is good at the outside box, then identify which pair is feeding to the inside. Then try each pair of screws (using the black and yellow) on the jack in question until it works. There is a correct polarity but the phone should work either way on newer phones. You can get a handy Radio Shack tester for under five bucks that shows if the line is working and in proper polarity and check all of your lines. I would suggest putting on a new jack but it looks like the old one is recessed in the base board.
BirR55 (Hick Phone Hooker Upper!)
