AT&T deposit amount change after porting number across regions
I am a new at&t subscriber with a question at&t can't seem to answer. I went to an att store to establish an account and pre-order the iphone 4 and was told I needed to put down a deposit of $100. Fine, no problem. However, later in the process when I indicated that I wanted to retain my NYC number despite being in the carolinas, they indicated that the amount of the deposit would now be $500, as the result of being in a different region.
When I asked if I could establish my account with the carolina deposit figure (via a "temporary" number and then port/relocate the NYC number after the fact, they said "yes" but I would be charged the $400 difference retroactively. This didn't seem right. After calling att and speaking to several different departments, I received several different answers ranging from"no, you can't do it" to "of course, a deposit is a deposit". Does anyone know the answer? I am not trying to avoid a deposit, just pay the deposit I was assessed and retain my phone number of nine years.