Someone prank called me last night at ~1:00AM and woke me up.  First a
woman spoke saying she was from my citys police department and that
there was a break in at my business with several items stolen.  She
then said she was going to give the phone to an officer.  The so
called officer was a man who started describing the business, its
location, and specific items that were stolen.  It was obvious that
this person knew about the business and what was inside.  After a few
minutes it became clear by this persons increasingly absurd questions
that it was a prank call.  I suspect an employee, and want to find out
who this was.  I called my cell phone company and asked them if I
could get their number (because it was blocked).  They said I would
have to call the police and get some kind of legal document enforcing
them to disclose the phone number.

Can I call the police and start some kind of process to find out who
called me?  Would they even take me seriously?  I would think they
would be because someone was impersonating a police officer.  How do
you think I should approach this with the police?  I live in
California.

Dear johnmk,

What happened is phone harassment and it is illegal in CA. What you
need to do is simple. The cell phone company cannot give out the
number with out an official subpoena from the police. This is because
the restricted number is private information and telecom laws prevent
giving out information to anyone but the account holder of the phone
number.

Telephone Harassment
The commission of threatening, harassing or obscene phone calls is a
misdemeanor. Penalties increase with the frequency of such calls and
the location of the victim when receiving calls (i.e. workplace).
Relief may include temporary restraining orders, injunctions or other
court orders. Cal. Penal Code 653m, Telephone calls with intent to
annoy. See also Cal. Penal Code section 422-422.1.
http://www.privacyrights.org/ar/callaw.htm

Telephone Records
No information regarding calling patterns, credit or financial
information, subscriber services, or demographic data shall be
disclosed by any telephone company without first obtaining the
residential subscriber's consent. Exceptions include directory
assistance services, postal zip codes, collection and billing
materials, documents made available pursuant to FCC reporting
requirements and the names and addresses of lifeline customers for the
purpose of low-income assistance outreach. Cal. PUC, Article 3, Sec.
2891, Customer Right to Privacy.
Telephone companies may not include unlisted "telephone access
numbers" on lists they rent. Cal. Pub. Util. Code 2891.1 (Smith, 1992,
1994)
Telephone Solicitation
http://www.privacyrights.org/ar/callaw.htm

You need to call the non-emergency number of your local police
department and file a police report. Tell whoever answers your
situation and they?ll refer you to the proper dept.

Also, get a copy of your bill that shows the incoming call and time.
Document what was said, time and date of what you can remember. In
addition, any names given to you by the callers, especially if someone
identified himself or herself as a police officer. The more
information and proof you have of the call, the better.

See here for more:
http://www.privacyrights.org/fs/fs2a-cellcalls.htm

Also at that site:
?The law will vary from state to state, but in California a single
call******** I note this to the comment below by daniel2d, since in
CA, 1 call is enough to be harassment******** is enough to meet the
definition of harassment if the caller threatens physical harm or is
obscene. If the call does not fall into either of these categories,
the calls must be repeated to be considered harassment.
Intent is another requirement included in most harassment definitions.
The law generally requires that the harasser intend the calls to be
viewed as harassment. Because of the need to prove intent, you should
tell the harasser that you do not want to speak to the person and to
stop calling. If the harasser persists after this clear message, it
will be easier to prove that the intent was to harass.?

The police will file a report, subpoena the phone number, find out
whom the caller was, and take appropriate action per the law. If you
get anymore calls during the time of the investigation, document them
as well and notify the officer in charge. Ask them for what they need
from you. They?re good at walking you through these situations. It?s
their job! They?ll definitely take you seriously.

Google search used: 
://www.google.com/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=phone+harassment+california&spell=1
phone harassment California

If this answer requires further explanation, please request
clarification before rating it, and I'll be happy to look into this
further.

Nenna-GA
Google Answers Researcher

A one time harassing telephone call is one thing.  They would probably
tell you to start keeping a log if it happens again - and then they
could institute an investigation for telephone harassment.

Proper process to follow:
Contact your local police department and tell them you have received
unsolicited (threatening) harrassing phone calls. Be sure to tell them
you are willing to press charges when this person is apprehended.
Tell them you would like to have a "Trap" installed on your telephone
line. They will give you directions and necessary codes to contact
your phone company and to this installed. The phone company will not
do this without police dept. authorization. This is really a very easy
process.
The next time this caller calls you will leave your telephone off the
hook and call police station form another phone line.The police will
contact phone company and request a trace for the number.. Wallahh!!
Hope this helps.