You may not be well-familiar with Rebtel, but the company is currently the largest independent mobile VoIP provider now that Skype is under the Microsoft umbrella. Rebtel, which routes international calls made from mobile phones and landlines to local numbers (specifically to minimize the cost of calling abroad), counts more than 13 million connected users and offers its services in more than 200 countries around the globe. (Not to mention an expected run-rate of $75 million by December of this year — and profitability since 2010.)

When Robin interviewed Rebtel CEO Andreas Bernstrom back in June, he expressed respect for companies like Viber “and the speed at which their mobile applications have gone viral”, but he held that dependence on WiFi and 3G would continue to “make for a poor user experience”.

“VoIP is essentially an improved fixed line service”, Bernstrom continued. “Mobile VoIP, however, has not been cracked due to the limitations of the data network”.

Well you can guess Rebtel has had a little something to say about that. The company launched its first versions of its iPhone and Android apps in 2010, followed by Blackberry in 2011, and today is announcing the launch of version 2.0 of its free iPhone app, which allows users to make and receive free international calls using WiFi, 3G, or local minutes. The app also allows texts and calls to be made to any non-Rebtel users (on any phone) for what Bernstrom says are 90 percent cheaper rates than standard international calling on an average carrier.

And perhaps the coolest feature of Rebtel’s app is a new proprietary technology called “KeepTalking”, which allows users to transition (mid-call, mind you) from WiFi/3G to local minutes. The iPhone and desktop apps will add to the Rebtel free call network already including Android and Blackberry apps, as well as facilitating free calls between existing platforms.

With the mobile VoIP market expected to reach $36 billion in revenues by 2016, and with 70 million mobile VoIP users expected to be in operation by the end of the year, Rebtel’s ability to call any phone or PC anywhere over WiFI/3G or local minutes and seamlessly switch between them if coverage deteriorates, seems to lend it a significant value proposition.

What’s more, the app also enables platform-independent free calls between Rebtel users, labeling these contacts as “free” in the app’s contact list to make it easy to see who’s already using the service. Whenever someone downloads Rebtel, the app automatically sends you a push notification and enables SMS to any mobile phone number, with an average cost savings of over 60 percent, according to the Rebtel team.

For more, check out the Rebtel app here.

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