About the limitations on multiple payments in a month
Online payments allow you to make multiple payments but each payment must be more than $.01 and full payment is still required by the due date. For example, for a $60.00 bill, you may pay $20.00 today and $40.00 next week as long as the total $60.00 is paid by the due date.
To pay online, sign in to your online AT&T account and select Make a Payment.