Certain recurring charges are billed one month in advance. These include custom calling features, calling plans, local calling services, and emergency 911.
Charges for local usage, long distance, and pay per use are billed in arrears (after the fact).
Your promo credits may have expired on your most recent bill.
It may take one to two billing periods for discounts to appear on your bill. Please pay the full amount on your bill, by the due date, to avoid future billing issues.
It might benefit you to have a plan for international calls (PDF, 237KB).
Taxes may apply to charges for products and services included in your bill. Specific taxes vary by state and locality.