8x8 X Series - X Series connects teams across channels and around the globe, giving you access your most critical information securely, from any location.
Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Vonage Business Communications - Vonage Business Communications transforms communications and activates conversations anytime, anywhere. Learn more about unified communications now!
Linphone - Linphone is an internet phone or Voice Over IP phone (VoIP).
CallFire - Grow your business with virtual phone numbers, IVR, voice broadcasting, mass text messaging services and power dialing.
MicroSIP - MicroSIP is a free portable SIP softphone for Windows based on PJSIP stack.