Twilio - Brings voice and messaging to your web and mobile applications.
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
Plivo - Plivo simplifies your customer engagement.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Telnyx - Telnyx is a cloud-based platform that offers access to carrier grade voice services over the internet.
Podium - Podium helps your business get more customer reviews, manage customer feedback, customer interaction, and online review management from one software.