Reserve a Specific Phone Number

I want the specific number [edited for privacy – please do not post personal information]. It is unused and owed by Pacific Bell, i.e. AT&T. I have an address located in Monterey, CA, where the number is associated with. I eventually want to change this number for cell phone usage. I have been told by two different representatives that AT&T can't give me this number, but they don't know why. What do I do?