FusionPBX can be used as a highly available single or domain based multi-tenant PBX, carrier grade switch, call center server, fax server, voip server, voicemail server, conference server, voice application server, appliance framework and more. FreeSWITCH™ is a highly scalable, multi-threaded, multi-platform telecommunications platform. It provides unlimited extensions, voicemail-to-email, music on hold, call parking, call center, call queues, phone provisioning and many other features. It provides the functionality your business needs and brings corporate level phone system features to small, medium and large businesses.