Ring to c/s is best... the installers sometimes write then on the work order that you got originally, but different people set them to different things when they have them installed. One of my boxes was set to 5555 (easy to remember), one was 2003 (year it was installed) and the other one the installer asked me what i would like for a pin number.
Trying things probably won't help much, so give c/s a quick ring and they can tell you... they'll be there until 8pm
MB