I need some help. I live in a 2 bedroom apartment and the phone jack in one of the bedrooms does not work. Meaning it has no dial tone. I did some surfing around trying to find out what is going on. My initial suspicion was that the previous tenant had a second line in that room so I was going to see if I can simply flip the red+green with yellow+black. However when I opened up the jack I discovered that there are only three wires running. The red, green and yellow. There is no black. :( I have not seen that covered in the pages I found on the internet.
Some of the things I tried were:
1. Open the other jacks to see how they are wired. They also only have three wires running to them and appear to be using the red+green.
2. I purchased a new wall plate thinking that maybe the contacts that the painters paint over were bad. But no luck so far.

Does anyone have any ideas for me? Anything to try?

Thank you in advance for your time.