i tried to call this number back but it says it's not in service
 Jul 07th, 2011
This is the Caller ID for Anthem Blue Cross of California's Technical Support Team. It is a legit call.
 Mar 17th, 2011
I was just talking with Anthem Blue Cross, and after finishing and hanging up, I got an incoming call a moment later.
It was from (805) 999-9999 which I thought looked a bit too much like a number that would not be possible for anyone to actually have as their phone number. So I didn't answer. Given the comments from other users ( at ) , I'm sure it was in fact Anthem Blue Cross calling back, for whatever reason, however, they did not leave a message. So it is possible it was a coincidence and it was an unrelated company.
Anyway, while it was still ringing I started searching for info on 805-999-9999
(which among other answer sites also led me to a web site
[ , which *seemed* to be a legitimate web site for a couple of realtors ... ]
with 999-999-9999 as the number to call if you wanted to do business with them ... which led me to search for details on the 999 area code also.)
So after also searching for details on 999 area code
(999 is the area code a company uses to conceal their geographic location
[ even if the rest of the number is a valid number, and the business is legit ... sort of in the same way that 800, 866, 877, 888, etc, could be anywhere in the USA ... A valid scenario would be a company that has a toll number as well as or instead of toll-free, but they have thousands of locations across the USA, the 999-(legit number here) number they have would be for the central office which has the goal of routing callers to the appropriate local office...]
as 999 is non-location specific... it is simply anywhere in the USA,)

it seems clear that no matter what area code (999 or otherwise) a 999-9999 is a spoofed caller ID number.

However, the reason for the spoof may be completely legitimate.
Apparently, it seems common that a VoIP (Voice over Iinternet Protocol) phone system may have 999-9999 as the default phone number set within the system when it gets installed, and the company's phone system administrator or IT tech guy is expected to adjust the caller ID number to whatever number is desired (which we would expect is the actual calling number in the case of a legitimate company.)

But, in legitimate cases, it may be that the company does not have an IT tech guy with an appropriate skillset to adjust the default caller ID number, (or even know it should be changed) and thus it never gets changed.

In other cases, there may be a fully appropriate skillset for adjusting the number, and they may want to keep the number hidden (or change the number from their real number to the 999-9999 in the case that their VoIP system did not have it set as the default) for their nefarious purposes.

The bottom line is that 999-9999 (regardless of the area code) could be anyone, and could be legit or otherwise.
If you are expecting a call and you know in advance it will be normal to see the 999-9999 on the caller ID, answer as usual.

If you are not expecting the call, play it safe and don't answer. If it's legit, they should leave a message... otherwise, it must not be important even if legit.
 Feb 01st, 2010
They keep calling and calling from different 310-805 numbers, interspersed with 999-999-9999 numbers. When I or the answering machine pick up, there's silence followed by the dial tone. When I call back, I get a recording saying "delay 4 not created", then a busy signal, then a hang-up. Exasperating!!!
 Dec 11th, 2007
This "CALIFORNIA" number calls several times a day and I do not dare answer. It is a (310)805-#### , the last 4 digits are always different, so I can not block them. Also, this number takes turns with another unwanted number during the day, 999-999-9999. Going on a week now.
 Dec 11th, 2007