Wal-Mart Stores shoppers can now buy Skype hardware and pre-paid voice-over-IP calling cards in about half of Wal-Mart's stores in the US.

While some Skype gear has been available for more than a year in some Wal-Mart stores, the expansion to 1,800 stores for Skype hardware sales and the addition of $20 Skype pre-paid cards shows the rapid growth of consumer VoIP adoption.

Skype competitor Vonage also sells products in Wal-Mart stores, but Skype will be first with the pre-paid cards, a Skype spokesman said.

"We have taken a sharp focus to launch the products and brands that consumers are moving toward at the most affordable prices," said Wal-Mart spokesman Kevin O'Connor. "The Skype hardware and pre-paid cards are a great fit with Wal-Mart."

Skype, an eBay company based in San Jose, has about 196 million registered users globally. The new $20 cards can be redeemed for international calls at rates as low as 2.1 cents per minute