Jaxtr, a Silicon Valley-based service that enables cell phone users to place free international calls via the Web, said its membership has doubled to 500,000 users in the past month.
Jaxtr said on Sunday it is signing up new users on the Web at a rate of more than 12,000 a day. The service allows cell phone callers to bypass hefty international calling fees using so-called voice over Internet Protocol (VoIP) technology.
The Menlo Park, Calif.-based company is one of several Web phone services to emerge over the past year that let users call from phone to phone for free or at vastly reduced rates to friends or family or business associates overseas.
Jaxtr, along with rivals Jajah, Jangl, Rebtel and GrandCentral, which Google recently acquired, are inspired by the success of Skype, which has attracted 220 million users who make calls between computers and phones.
"No download is required, and our direct numbers can be dialed from any type of mobile phone or even ordinary landline phones," Jaxtr Chief Executive Konstantin Guericke said, contrasting its Web-based approach to certain complexities of other services.
"VoIP has cut the cost of making calls, but it has pushed up the cost in terms of customer inconvenience," he said.
Jaxtr said it was expanding the number of countries where it offers local, direct-dial phone numbers by 18 including China, India, Russia and Germany in addition to the initial 29 where it offered services including Britain, Canada, France, Japan, Nigeria and the United States.
It also is adding South Africa, Argentina, Peru, Colombia, Venezuela, Dominican Republic, Honduras, Panama, El Salvador, Jamaica, Estonia, Latvia, Slovenia and Hong Kong, it said.
The service lets friends call from overseas using local numbers without incurring international charges. Recipients can take calls on conventional landline or cell phones.
Jaxtr members feature links to Jaxtr on their personal Web sites. Callers who wish to reach them enter their own phone number on the Web page and press a button to initiate a call. Using the Internet, Jaxtr's computers act as an intermediary to set up the call automatically between the two parties' phones.
Once the initial Web connection is made, callers can speak for free up to 100 minutes a month. Jatxr eventually plans to charge for additional services it has yet to announce.
To receive calls, one can sign up for the service at Jaxtr's Web site. They can install a bit of code that links to the Jaxtr service on their own personal sites, including many of the popular social-networking sites such as MySpace, Facebook, LinkedIn, Flickr or AIM.
Jaxtr's strategy has targeted heavy Web users on blogs or social-network sites. By contrast, its closest rivals, Jajah and Jangl, have focused on partnerships with major Web sites or in the case of Jajah, with Intel and Deutsche Telekom.
Guericke joined Jaxtr in late 2006. He was previously co-founder of top business-networking site LinkedIn.