Billing
Software was created in order to handle billing and time tracking as well as
invoicing the customer for products and services. This software can also track
worked hours by employees, as well as the expenses related to projects or
clients.
Obviously SIP is considerably better than H.323 and complies with the understanding of IP-telephony as a global mass IP-service, and it should be implicitly considered right this way. And as SIP is able to serve not only telephony but also any communications at all in the real time over the IP-protocol; obviously it should become a base for other IP-services not yet existing but will appear in the future, as well.