It can be very frustrating not to be called back.  However, there could be a
valid reason. Too often you call and ask for information that is important to
you.  The hiring authority does not see the benefit to
them to call you back.

Rather than asking for an update, offer
to provide them with additional information.  Instead of asking a question,
offer new solutions to their problems.  Instead of an email, send them
additional positive references.  Instead of asking for information, send samples
of your work.

• Hiring authorities will call you back if they see the benefit to them.
• Hiring authorities will call you back if they think you will make them look
  good.
• Hiring authorities will call you back to obtain additional information.

Leave a different message and you WILL be called back!