Computer- and network-based methods and systems for transmission-based billing are provided. Example embodiments provide a Packet-Based Billing System ("PBBS"), which enables application providers, such as carriers and content providers, to bill subscribers for the use of content on mobile subscriber devices, such as wireless devices, on a per-application, per-user basis based upon the extent of the usage. Embodiments of the present invention can also be used to bill subscribers for the use of content on a per-application, per-user basis for wired subscriber devices as well, using the same techniques. In operation, the PBBS provides modified content by inserting billing and tracking code into content returned to a requesting device. The modified content, when executed, tracks the amount of data sent and received between the content and a network and posts the accumulated data to a proxy/billing server according to business rules for an interval/frequency to post such data. The proxy/billing server stores the raw billing data and an accounting program retrieves the billing data to generate customer (call) data records. Business rules that specific different charges for different content or users can be incorporated into the system.