The Sinch SDK for iOS lets developers add voice calling and instant messaging capabilities to their iOS based mobile apps. The SDK handles signaling and audio management. In addition it offers support for:
App to app calling
App to phone calling
Instant messaging to single and multiple recipient
Collaboration company 37Signals bought the popular Ember iPhone app, which uses the company's Campfire API (our Campfire API profile) to display and update chats. The app has been renamed 37Signals Campfire and is now available for free (previously $9.99).