WikiPro - All-in-one Business to Customer Communication
Twilio - Brings voice and messaging to your web and mobile applications.
Respond Flow - The Mailchimp of SMS
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
Proximiti MessagePro - MessagePro services include business SMS, secure messaging, interactive messaging, BOTs, scheduled messaging, and fax. Solutions for SMB and enterprise.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.