8x8 X Series - X Series connects teams across channels and around the globe, giving you access your most critical information securely, from any location.
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
Vonage Business Communications - Vonage Business Communications transforms communications and activates conversations anytime, anywhere. Learn more about unified communications now!
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Broadvoice - Cloud PBX solution for SMBs
Sipdroid - Free and open-source SIP/VoIP Client