  Next generation networks (NGN) services are assumed to be a new revenue
stream for both network operators and service providers. New services
especially focused on a mobile telecommunications that would be used not only
as a communication de vice but also as a personal gateway to order or consume a
variety of services and products [1]. This type of advanced services can be
accomplished when the adaptability of the packet-networks (Internet) and the
quality of service of the circuit switched networks are combined into one
network [2]. New challenges appear in the billing of this heterogeneous multi
services network. Some examples of such a services and possible solutions about
charging and billing are examined in this paper. The first steps of
mathematical model for billing are also considered.
