Twilio - Brings voice and messaging to your web and mobile applications.
Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
BulkSMS - SMS messaging service provider offering two-way SMS communication services.
Plivo - Plivo simplifies your customer engagement.
Podium - Podium helps your business get more customer reviews, manage customer feedback, customer interaction, and online review management from one software.