Twilio - Brings voice and messaging to your web and mobile applications.
MyOperator - MyOperator is a cloud-based call management system for voice communication purposes.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Servetel.in - Servetel is an Indian cloud telephony service provider. We provide services such as Toll-Free Number, Virtual Number, IVR, Bulk SMS and Voice Broadcasting.
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.
Vibtree - Communicate on Cloud