VoIP Simulation

I am looking here best simulation application for VOIP.I am working on my academic project for which i need VoIP Simulation so please provide me such application best if working on windows environment but not problem for else .
thank you

I don't think that VoIP software Simulation is available to configure the actual device well check for Packet Tracer i am not sure...

well dont found any such application but there are several commercially available products that can be use on network and used to test and report voip and network capability.