i have called a number of agencies (ones that are currently popular in Chicago) and have not gotten any call backs.  I even had one pick up yesterday and she said she would call me right back and never did.  I wonder if there is something about my phone number (the account is registered to a PO Box).  Is there a way that I can play the game without getting a new phone or messing with my phone account?

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Your phone, like you said may be a problem; just like lot of places won't respond to "blocked numbers"
You might have better luck emailing them or submitting an online screening form:
This is what I copied and pasted from one of the Chicago agency's website:

"All potential clients must be pre-screened, this process is quite simple. Please call or email us with the following information: Full Name, Profession, Company Name, Address and Main Phone Number along with your ext. if applicable (No Direct Lines). An alternate phone number where you can be reached is required as well. Absolutely No Exceptions.

A P.O. box is normally used by people with something to hide, and if that is what your phone number is connected to, there is your answer. You need to join preferred411.com and get a hobby phone. A hobby phone is a track phone you only use for providers and leave it somewhere safe.

great.  thanks for the tip.  i'm gettin it together now.  

thank you lovetodaty!  i appreciate the help