Saleem – unless Qtelnet have some other manual except the user guide available on their site – it looks like the billing/provisioning functions are very, very, very basic.
May be it is good as a traffic convertor, but if you want a real billing – look somewhere else. Have you seen PortaBilling (www.portaone.com)? Their billing is really nice, and there is SIP server for it – PortaSIP (based on the proven-to-work components such as SER, VOCAL, …)