Zoiper - Cross-platform VoIP softphone dialer for SIP and IAX systems
Twilio - Brings voice and messaging to your web and mobile applications.
Ekiga - Ekiga (formely known as GnomeMeeting) is an open source VoIP and video conferencing application for...
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
SolarWinds VNQM - VoIP monitoring software
BulkSMS - SMS messaging service provider offering two-way SMS communication services.