Skype is riding a VOIP wave it helped create with free computer-to-computer calls, but it's far from being alone in the fast-growing industry Skype users in the U.S. and Canada can call free to regular landline and mobile phones anywhere in those countries until the end of the year, the Internet voice company said Monday.The company, based in London and acquired last year by eBay Inc., has built its business on free calls among PCs and other Internet-linked devices using free Skype client software. To let Skype users reach regular phones from the Skype client, the company offers a paid service called SkypeOut. Now, North American users won’t even have to pay for SkypeOut calls — at least until the end of the year. The special offer is limited to users within the U.S. and Canada calling phones in those two countries.Skype is riding a VOIP (voice over Internet Protocol) wave it helped create, reaching 100 million registered users on May 1, according to the company. But it’s far from being alone in the fast-growing industry. Competitors such as Vonage Holdings Corp. offer unlimited domestic calling to any number for a set monthly price. Vonage offers a residential unlimited calling plan for US$24.99 per month and a small business unlimited plan for $49.99. The company has been competing for users with its own promotions lately, on May 1 waiving international charges to its unlimited-plan customers for calls to landlines in five countries: France, Italy, Ireland, Spain and the U.K. Users of all of Vonage’s plans already can call Canada and Puerto Rico without international charges.In addition to low cost, VOIP can provide special features such as Web-based voice mail, real-time online billing data and a choice of area codes. Last week Skype introduced a new version of its software with new capabilities including SMS (Short Message Service), integration with Microsoft Corp. Outlook contact lists and payments via Skype.More than 5.4 million U.S. households subscribe to a VOIP service, compared with just 2.7 million a year ago, according to an estimate by research company Telegeography, a unit of PriMetrica Inc. Technology Industry