This number usually appears as an Unknown caller because the phone lines that are associated with this number are from a high-security office. If you know someone that works for the government or Boeing or some other high-security company, it could be that they're calling you so pick up!
General Contractors looking for and so on. Hang up. I try to get in touch with a real person. They hang up when I ask them if they looked up my number in the Do NOT call list.
I answered it but the connection was bad so I just said, "I can't hear you" and hung up. I already knew it was a telemarketer anyway because all calls I get from the 310 area code are telemarketing calls, mainly construction with a few so called duct cleaning ones thrown in. Also calls from 562 and 626 (my own) and 714 are always telemarketing calls.