Your Comcast / Xfinity account number is found on the top-right corner of each bill you receive, and there is one account number for each billing address. Your account number is created when you sign up for any Comcast service and does not change. Each XFINITY Voice account has a single four-digit Voice Security PIN that protects access to voice features online and over the phone. If you are a new customer, you should have received your Voice Security PIN via an automated phone call or by mail. Before you can access certain details about your voice service, including billing details, voice information and voice features, you may be asked to provide your Voice Security PIN. Online, your account number is associated with XFINITY usernames for each person on your account. Each XFINITY username has a contact email address, a password and a secret question and answer (in case you lose your password). The primary XFINITY username is the main username for the account.