KOOKOO - All in one solution for calls, IVR, live chat, customer management & more.
Twilio - Brings voice and messaging to your web and mobile applications.
Dialfire - Cloud Calling at Jet Speed
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
HoduCC - HoduCC is a FreeSWITCH based product which offers contact center softwares for call centers.
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.