The application launches initially for Citi MasterCard credit card holders, but Google also said Monday that Visa, Discover and American Express will be able to add their cards to future versions of Google Wallet.

The application, first announced in May, was described on Monday.

Google said it would begin rolling out Google Wallet to Nexus S customers through an over-the-air update; customers need to look for the "Wallet" app on the phone.

A two-minute video demo of the app is included.

"This is still just the beginning, and while we're excited about this first step, we look forward to bringing Google Wallet to more phones in the future," said Osama Bedier, vice president of payments at Google.