Twilio - Brings voice and messaging to your web and mobile applications.
Tatango - Tatango is a mobile messaging platform for agencies.
Bandwidth - Bandwidth offers SIP trunking, Emergency communications, and Voice & Messaging APIs.
Postscript - Like Mailchimp for SMS
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
Flowroute - Flowroute provides direct access to telephony resources - such as calling, messaging (SMS & MMS), call routing, SIP Trunking and Communication APIs.