From the start of telephony, every major carrier has protected its network behind a series of barriers: technical, legal and financial. Although some of the reasons for keeping their networks closed have some credence, such as security and reliability, it's pretty clear that carriers hold the opinion that opening up their network does not benefit them. As time has gone on, and technology has matured, the closed nature of networks is less and less about technical concerns, and more and more about carrier fear and an inability to present compelling business cases to customers.
With the GrandCentral acquisition, this has now changed. Google now owns a company that is a legitimate PSTN service with strong integration into open VoIP standards, and did it in a very Voice 2.0 way. GrandCentral currently supports free and unfettered SIP connections to Gizmo accounts, unlocking the entirety of the SIP architecture, benefits and approaches. And more so, GrandCentral has done this in a completely Web 2.0 manner, freeing itself from the chains of a technology play and firmly focusing on a valuable application that people will pay for.
Is this is the end of an era for closed telecom networks? Yes, I think it's the beginning of the end.