hi ibrahim,
as far as bandwidth goes for each voip line u will need about 100kbps other then that im trying to find about myself for network what is used in pakistan and whats the best and not so expancive way to go about it, and for PSEB goes they do require licence but its not that expancive or hard to get it i think its about 5000 to 10000 Rs a year fee for it but u might wanna get in touch with them yourself here the website http://www.pseb.org.pk
Good Luck
Asif