The number is listed at http://www.csbcorp.org/, the website of Community Service Building Inc. It's the phone number for their Facilities Assistance Center Team (FACT).
Actually, this is a central number for a huge set of offices owned by DuPont. If ANYONE calls you from the complex, your caller ID will show this number. If you call back to this number, you get the main voicemail system. So, blame AT&T. It is just a system shortcoming and I have had this issue with every AUDIX system in the world.