Aculab - Telephony platforms - cloud, hardware and software.
Asterix - Open source framework for building communications applications. (F)
Fonality - Cloud based VoIP Phone Systems, On-Premise Phone Systems, Collaboration Tools & Contact Center Solutions.
Grasshopper - Cloud phone system.
Line2 - is a cloud phone service that adds a second line to your mobile phones, tablets and computers with the simplicity of an app.
Ring Central - Cloud based PBX.
Skype - A freemium voice-over-IP service and instant messaging client. (F)
- Twilio - APIs for Voice, VoIP and Text across office locations and devices