DialogTech - DialogTech is an end-to-end call attribution and conversion platform.

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

CallTrackingMetrics - Know who is calling and how they found you. Maximize the return on your advertising.

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

Marchex - Marchex is a mobile advertising analytics company that connects online behavior to real-world, offline actions.

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.