Also, with AT&T you pay for the month ahead of time. Your first bill also includes on a partial month of service for your actual first month.
So... your bill is:
Activation fee
partial first month
first full month
taxes and fees
I don't have AT&T, but when I worked for AT&T Wireless, the billing was at the beginning of the cycle. Billing is due at the beginning of the cycle, however there is a grace period to pay before late charges are incurred.I don't know what plan you are on, but I pay for the previous month.
Example:
Billing Cycle for September ended on 09/26/07, and the payment for September is due 10/16/07.