BOSTON--A Swedish start-up company is rebelling against the wireless “cartel” in Europe and elsewhere, offering customers a way to use their mobile phones to make unlimited international calls on their mobile phones for $1 a week.

Rebtel was founded by Hjalmar Winbladh and Jonas Lindroth, who earlier founded Sendit AB, a mobile Internet software company acquired by Microsoft. In this latest venture, the two are using VoIP technology to enable consumers to use session initiation protocol-based technology to make cheaper international calls. Their target audience is ex-patriots, small businesses with international ties and corporate rebels.

“VoIP lets you de-couple the voice service from the network,” Winbladh said. “We have found that people would rather talk on their mobile phones than on their PCs or their fixed phones. In the world today, there are 2.5 billion cell phones and only 500 million PCs.”

Rebtel’s service, available in 35 countries today, starts by assigning local numbers to international calls. A customer logs on to www.rebtel.com and signs up, putting in his or her own phone number and the international number of the person they want to call. Rebtel assigns local numbers to each, in the appropriate company, and sends SMS messages to each on their mobile phone, so that each half of the calling duo can save the new phone number in a mobile address book.

One party then initiates a call to the other, but the called party hangs up and then dials back. Rebtel’s session control software server is able to hold onto both ends of the call and connect the two parties in a VoIP call that doesn’t generate interconnect fees on either end.

“Interconnect fees are very high, particularly in Europe,” Winbladh said. “International roaming is very expensive. This way, you are using minutes from your bucket of minutes, and that is all.”

The company uses partners--Tier 2 and Tier 3 VoIP providers--to gain access to local numbers in the 35 countries it serves.

Rebtel is targeting the very large ex-patriot community with a service that Winbladh believes can turn a profit. Callers can also choose a “Reb-out” service, which uses the local number but doesn’t involve hanging up to initiate the VoIP call. Those calls are billed at the prevailing cost of interconnection, which can vary from pennies a minute to as much as 25 cents a minute in Sweden.