Rebtel gives apps a voice with new developer platform

Rebtel, the mobile VoIP challenger to Skype (s msft), is opening its service to developers with a new Rebtel Voice platform for iOS (s aapl) and Android (s goog). The new SDK, which is launching in private beta Tuesday, will allow developers to easily voice-enable their apps with about 15 minutes worth of work.

This will allow synchronous communication for gaming or social apps so users can talk app-to-app while they play came or share photos together. Or it could allow other apps to easily add support for free calls to customer support. That could make apps more engaging, potentially making more money for developers.

Rebtel’s SDK could also be used by developers to create their own branded mobile VoIP app without building their own back end. Messaging apps could easily add voice service using Rebtel, which also allows them to call fixed phone numbers.

Rebtel, VoIPThe calls are carried over Wi-Fi or 3G and offer HD voice quality. Users don’t have to be Rebtel members, they just press a “talk” button in their app. The service is free for now, though Rebtel may look at charging later for apps that do a certain amount of volume.

Rebtel is starting slowly, testing the new platform with just three companies including VIVfone, which makes a mobile CRM app, and MobisleApps, which develops lifestyle, dating and productivity applications. Rebtel is looking at learning what developers want through its private beta before opening up the service next year.

Rebtel CEO Andreas Bernstrom believes there’s a big opportunity in connecting mobile apps via voice. He said developers have been looking for a way to add a voice layer to their apps without having to do a lot of the work. And he believes that can ultimately help Rebtel by introducing the service to a lot of new customers. Rebtel currently has more than 17 million users and is on pace to generate $80 million in revenue this year.

Rebtel faces some competition from services like Twilio, Skype and WebRTC, an emerging technology that will enable voice and video calling from any browser. Joyn, a rich communication technology from the GSMA that is backed by big carriers, can also be used for in-app communications. The rise of these services comes as mobile users spend less on voice and text messaging as they move to more over-the-top voice and messaging apps. The promise of Rebtel’s SDK hinges on the belief that people want to keep talking by voice, but they’d like to do so in the context of existing mobile apps. That might work in some situations though it’s unclear how many apps will really benefit from synchronous in-app voice calling.