To troubleshoot this kind of problem, you need a continuity checker (from the hardware store) and some basic techniques. First, unplug all phones or other devices plugged into the phone system. Then you need to find the phone junction box and disconnect the incoming phone line from the phone company. If you put the continuity checker on the connectors that feed into the house, you should see that current is flowing. If not, it means one of your phones or other devices is the problem, and you can use trial-and-error to determine which one it is (by selectively unplugging them and testing with an incoming call). Assuming the short is in the wiring itself, your continuity checker will keep lighting up until you locate the offending circuit. Disconnect each circuit from the junction box in turn, until the continuity light goes out. When that happens, you've isolated the bad cable. Then, plug all the phones back in, hook up the incoming service again, and see which phone has no dial tone. That's the phone that's on the circuit that is shorted out. Now you either have to replace that wire or find the short by other means -- i.e. inspect it, or divide-and-conquer with the continuity checker, etc. If all this seems too daunting, get a handyman to come in and do it.

I'm just wondering why I can call out, but people calling in can't get through.