The invoice configuration is available in the administrative area, under Setup -> Invoice Setup -> Invoice Setup.
Bill to company name - This determines wether the invoice always display the customer's name (configuration value of No) or if the account has a company name, to use it instead of the customer's name (configuration value of Yes.)
Currency Symbol - This is the currency symbol to be used on the PDF invoices.
Currency Decimal Precision - This is the number of decimal precision to use on the PDF invoices. Typically a value of 4 or 5 is used, since rates are usually fractions of a US cent.
Number of items to display in summary - This is the number of summary items to display on the first page of the PDF invoices.
News you can use - This is an advertising and/or notice to be shown on the first page of PDF invoices.
Page Type - This is used by the PDF invoices to determine which PDF template to load. This value will always be 1, unless specified otherwise.
Default Invoice Delivery Method - This determines the default method used to deliver the PDF invoices. It may be configured as None, Email, and Print.
Show itemized detail pages - If this is Yes, then the users calling detail records are enumerated on their PDF invoice.
PDF Invoice Plugin - This is the PDF invoicing plugin to use when generating PDF invoices. For AgileVoice, you would typically choose voip, but you might have a look at the voip-detailed.