I'm curious if the writer of this article didn't quite understand the technology: According to this piece, Calypso is marketing a platform that will route calls from a Calypso cell phone over Wi-Fi to a cell phone network. I'm guessing that in reality, Calypso is marketing a platform that offers voice over Wi-Fi when in range of a Wi-Fi network as well as voice over regular cellular networks. Calypso's Web site doesn't go into much detail about how its technology works.
China Telecom has spent $500 million on Calypso's platform, which is described here as delivering voice over Wi-Fi and cellular.