New data from TeleGeography show that the growth of international telephone traffic has slowed, while Skype’s growth has accelerated.

Over the past 25 years, international call volume from telephones has grown at a compounded annual rate of 15 percent. In the past two years, however, international telephone traffic annual growth has slowed to only 8 percent, growing from 376 billion minutes in 2008 to an estimated 406 billion minutes in 2009, according to recent TeleGeography research.

The deep recession has had a marked impact on many routes. "Demand for international voice has been remarkably robust, but it’s clearly not recession-proof," said TeleGeography analyst Stephan Beckert.

“While international telephone traffic growth has slowed, Skype’s traffic has soared,” he added.

Skype’s on-net international traffic (between two Skype users) grew 51 percent in 2008, and is projected to grow 63 percent in 2009, to 54 billion minutes. That means that about 13 percent of international calls are made on Skype.

"The volume of traffic routed via Skype is tremendous. Skype is now the largest provider of cross border communications in the world, by far," said Beckert.

He claims that the proliferation of alternatives to telephone calls—including Skype for mobile devices, and Google’s gradual entry into the voice market—will present ever greater challenges to international carriers.