Hjalmar Winbladh, CEO of the VoIP startup Rebtel, is building a business based on the strategy of making international mobile calls at local rates by circumventing wireless operators' interconnection fees.

"We're building a relationship with real customers," Winbladh said Monday (Nov. 12) as huge ferry boats steamed by the company's offices in the southern part of the Swedish capital.

The service works by callers providing Rebtel with the mobile phone number of an overseas friend. The company then provides a local number that allows users to call back at local rates. The service leverages callers' free minutes for local and weekend calls to complete the connections—minutes that often go unused, are not rolled over and are lost each month on the bottom line of mobile carriers.

The cost of international calls is in routing the call to a mobile phone. Rebtel provides callers who sign up with a local number to dial, then routes the call via the Web. Hence, international calls that can cost tens of dollars per minute on most mobile services cost pennies.

Winbladh said the service has so far been rolled out to 42 countries and that traffic on its network is increasing steadily. He said the average Rebtel call lasts about 13 minutes.

The company is using viral marketing techniques on the Web to attract ex-pats and foreign workers based in the U.S. and Europe. A network display in Rebtel's office showed network traffic climbing between the east coast of the U.S. and hot spots like India.

Winbladh sold his previous startup, Sendit, to Microsoft in 1999 for $150 million. It has so far raised about $20 million in venture capital. Next, Winbladh said Rebtel will offer roaming and small business services.