The golden age of standalone VoIP seems to be coming to a close, heralded by the sale of longtime VoIP provider deltathree Inc. (DDDC.OB) to a multilevel marketing firm best known for testing regulatory and ethical boundaries worldwide.

Last week, embattled deltathree announced it had sold itself for 42 percent of its market value to American Communications Network (ACN). ACN is the same company that tried to buy defunct Trinsic Inc. at auction in 2005. ACN hawks its products through “independent representatives” and has been taken to court in several countries for deceptive marketing and business practices.

The sale of deltathree to this particular company, then, is a curious one, as ACN already offers digital voice service, along with a video phone. So the question becomes whether ACN will use deltathree for its customer base, for its patents or for R&D.

Another question is how this apparent dissolution of deltathree will affect the rest of the standalone VoIP industry. Analysts aren’t too keen on companies like Vonage Holdings Inc. (VG), now that big telcos and cable operators are offering VoIP as part of their service bundles. Is the sale of deltathree a harbinger of things to come?