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

CALLR - CALLR is an extremely helpful app for those who have to deal with call control protocols for their business. You can create a customized call control system that will perform a wide range of functions.

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

MeetingMogul - Join any conference call with one-touch

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.

CamCard - CamCard reads business cards and save instantly to phone Contacts.