CAMBRIDGE, MASS. — Could it be that Sky Dayton is feeling a little lonely? EarthLink, the company he founded, refused to participate in the latest round of financing for Helio, the upstart wireless carrier he now heads. In a keynote speech at Technology Review's EmTech conference, he touted his company's service not as, say, letting you make calls and surf the Web, but "connecting you to your community of friends." So it's a social network! Ah, but a social network that requires buying a phone (as much as $295) and signing up for service ($85 to $90 a month, on average). No wonder Dayton's ersatz social network, cleverly disguised as a cell-phone company, only counts 140,000 users, and is losing hundreds of millions of dollars. Somehow I don't think Facebook CEO Mark Zuckerberg is sweating over this one.