Nexmo - Nexmo is a simple two way SMS API with global reach and wholesale rates
Plivo - Plivo's Voice API enables businesses to build Voice apps to reach customers globally in 200+ countries. Try Plivo's Voice API for free. Instant Sign Up.
Clockwork SMS - Clockwork is an Easy Text Message API. An SMS API for Developers. Build powerful apps and include SMS. Signup is free, Try it now.
MessageBird - Reach 7 billion phones in seconds via SMS, Chat & Voice. Try it for free and improve your communication.
BulkSMS - SMS messaging service provider offering two-way SMS communication services.
Infobip - A2P messaging platform for enterprises, resellers & mobile operators with global network coverage.