There’s no question that social networks are used by millions upon millions of people around the globe. What’s amazing — and inconceivable in times past — is that these services are available for free to anyone who wants to use them.  Even entire companies are tapping into these offerings to drive their collaboration efforts.

With the old-fashioned saying in mind of “you can’t get something for nothing,” this begs the question of who is really paying to keep all these great services afloat and functioning.  Can you imagine if the original phone network, Ma Bell, offered everything for free from day one?  Remember, Facebook, Twitter, and YouTube all require huge data centers staffed by highly competent IT professionals to keep things running 24 x 7.

The assumption has always been that advertising would support these services, in the same way it has provided us radio and television. Google, MSN, and Yahoo, for example, rely on the online ad model, which has proven effective.

However, research firm IDC questions if advertising can really work effectively in social networking environments such as Facebook and Twitter. In a new study, the consultancy suggests that it may not. “Advertising does not factor into consumer motivations” on social networking services. Social networking is used for communication, and that’s about it. “In fact, users are less tolerant of [social networking] advertising than the best-tolerated forms of online advertising,” IDC says. “Ads on SNS have lower click-through rates than traditional online ads (on the Web at large, 79% of all users clicked on at least one ad in the past year, whereas only 57% of SNS users did), and they also lead to fewer purchases (Web: 23%; SNS 11%).”

“Social advertising” — in which ads are targeted to users’ contacts — may ultimately be more effective than behavioral targeting, IDC suggests. However, it adds, “that idea is stillborn. Of all U.S. Internet users, only three percent would allow publishers to use contact information for advertising.”

There is a natural reflex to view intrusive ads with disdain — remember the visceral reactions to pop-up ads in the early days of the Web? However, attempting to charge for services may also run into opposition. Facebook, for example, has gotten flak on some initiatives.  The blog-creation service Tumblr also recently announced it would offering a “premium” service to fund the venture.

Overall, however, advertising seems to be the only logical way to fund and monetize social networking services — if it can be done non-obtrusively, and with respect to privacy concerns. IDC suggests that this may work for social networking services if they “become more like portals, such as Yahoo! or MSN, and they will come closer to the audience reach of the top services.”