Tragofone - White-label VoIP Softphone with WebRTC and Auto-provisioning
Twilio - Brings voice and messaging to your web and mobile applications.
PhonerLite - PhonerLite enables your PC to use it for internet telephony (VoIP , Voice over IP, SIP).
Plivo - Plivo simplifies your customer engagement.
tSIP - tomeko.net/software: SIP client for Windows.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.