TollFreeForwarding - TollFreeForwarding offers hosted PBX, call forwarding and IVR solutions.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Loop Communications - Loop Communications provides hosted VoIP business phone systems to small businesses and mid-sized companies.
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Vonage - Vonage is a cloud-based all-in-one VoIP software solution designed for multiple industries such as accounting, healthcare, finance and marketing etc.
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.