The staggering variety of free stuff available on the Internet sometimes seems to have repealed the first law of economics: There"s no such thing as a free lunch. But as so often happens, the dismal science actually has it right. When it looks like you"re getting something for nothing, somebody is paying, and it"s often instructive to know who that is. I"ve been testing a new phone service called ooma that provides an interesting case in point. Once you pay $399 up front for a box called the ooma Hub and connect it to your phone and the Internet via your home network, you are promised free, unlimited phone calls over two lines, plus voice mail. The system works fine and is simple to set up. When a voice-over-Internet call has to go to a regular phone number, a service such as ooma usually has to pay a "termination fee" to a carrier such as Verizon. Skype, for example, charges 2% per minute for calls outside the Skype network. But ooma avoids this by using some of its customers— those who have kept regular phone lines—to serve as gateways onto the local phone network at no charge. When you want to call outside the ooma network, the call moves from your Hub over the Internet to a second landline-connected Hub within the destination"s local calling area. The Hub dials the target number and patches the call through. In effect, ooma customers with landlines pay to keep the whole system going. You don"t even notice if your landline is being used because your own phone calls go out over your broadband connection, with your flat-rate monthly phone bill covering the ooma traffic. In fact, this improves the efficiency of the phone system by putting idle lines to work. But if ooma ever gains real traction, I expect a legal assault from big phone companies, which are losing income from termination fees. Web services do take advantage of genuine economies. The phone network is more expensive than the Net. Lots of Net players build on these advantages. Skype relies on selected users who act, often without their knowledge, as "super nodes" to manage the system. FreeConference.com provides calls by taking advantage of regulatory quirks—namely, the stiff tennination fees long-distance carriers must pay to certain rural phone companies that handle calls into their territory. In effect, the free conferences are subsidized by customers and shareholders of the long-distance carriers. You may as well enjoy free calls while you can. But it"s always a good idea to read the fine print. If it isn"t obvious who"s paying for a free service, it might well be you.

【正确答案】 B

【答案解析】解析：推理判断题。文章第三段提到ooma是通过利用一些使用常规电话线的用户而提供免费无限制打电话的服务，故选B。A项“将ooma集线器连接到你的电话上”是使用ooma的操作方式，而不是免费无限制打电话的保证；ooma利用它那些接有常规电话线的用户作为本地电话网络上的网关，从而避免支付终端费用，故C错误：使用常规电话线的是用户而不是ooma系统软件，故D也可排除。