Twilio - Brings voice and messaging to your web and mobile applications.

Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.

Telnyx - Telnyx is a cloud-based platform that offers access to carrier grade voice services over the internet.

Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates

Podium - Podium helps your business get more customer reviews, manage customer feedback, customer interaction, and online review management from one software.

thinQ - Cloud communication platform