4PSA VoipNow ExpressScreenshot 

 

4PSA VoipNow is the leading IP PBX server software for Service Providers and enterprise. Easy to use and deploy, 4PSA VoipNow softswitch helps you increase productivity and reduce voice communication costs. 4PSA Express free edition offers standard PBX features, while Professional (commercial) edition supports more users, IVRs, calling cards, callback, remote conferences and call queues.

Screenshot of 4PSA VoipNow Express