Rebtel launches calling feature to add to apps STOCKHOLM (Reuters) - Sweden's Rebtel launched a calling feature which can be embedded in apps from games to dating services, a move which could help strengthen its user base and make it a more formidable rival to Microsoft Corp's Skype. Rebtel's new free voice platform, which can be used on both Apple Inc's iPhone operating system and by developers for Android phones, is intended to make apps more social and expand their reach. Rebtel has 17 million users and is the world's second-biggest internet calling service after Skype. Rebtel Chief Executive Andreas Bernstrom estimated that at least 10 percent of the 1.2 million apps in use would benefit from the call feature. "If we can get a tiny, tiny percentage to actually start using it, then there's going to be a lot of traffic going through our network," Bernstrom told Reuters. Europe's traditional phone companies are facing intensifying competition from Internet-based services like Viber and Tango as well as Skype and Rebtel. Skype, bought by Microsoft for $8.5 billion, now controls 25 percent of volume in international telephony. Rebtel combines internet calls with traditional calling and offers free calls between Rebtel users, but charges for calls outside its network. It is already profitable and is aiming for $80 million in revenue this year. Reporting by Mia Shanley; Editing by Tarmo Virki and David Holmes