I need a software tool which can emulate network impairments/jitters in the network and test VoIP calls behavior and quality.
I have used WanEM a few times and find it to be an acceptable entry level traffic generator.
While it doesn't beat a true hardware network emulator (like a Network Nightmare appliance, for example), I have found it to be an decent traffic generator and it does provide a number of knobs and dials to tune your traffic. As I understand it, this application is capable of testing VOIP as well.
Please note that this software is a bootable .iso meant for testing in the middle of a network test environment and is not available as a package installation. It can also be run as a virtual appliance within VMWare Player or Server.
If you can be more specific in your requirements, I might be able to provide additional resources.
Whilst not software AppView Voice is perfect for readiness assessments before deploying voice services. How many simultaneous voice calls can your infrastructure handle before quality issues occur, do you have enough bandwidth, where does latency and packet loss occur eg whose network.
Take a look AppView Voice.