Wheeler is wary about the security implications of peer-to-peer calling. "For consumers, [the networks] are great. On a business level, you have to watch them. There's also a business risk involved," he says.

With Skype, for example, calls are encrypted, but the encryption scheme has not been subject to open, public review. Skype, which uses multiple ports to get through firewalls, is particularly difficult to block. It also offers an application programming interface (API) that developers can use to create presence-aware applications that can traverse the Skype network. Since Skype supports file transfers, it's possible that "Skypecasts" could transfer copyrighted content into or out of the enterprise, says Lazar.

However, security concerns may be overblown. "If the flaws were easy to exploit, someone would have figured out how to do it by now," Lazar says.

Michael Jackson, director of operations at Skype, says the latest client disallows access to the API by default and allows the file transfer feature to be disabled.

Eventually, integrated clients within businesses will become common, says Lazar. For example, products like Avaya Inc.'s Converged Communication Server and Microsoft's Office Communications Server 2007, slated for release next year, offer a similar experience to services like Skype for internal calling. However, such products typically won't work with public peer-to-peer systems such as Skype.