Google's launched its Google Wallet service, an application that allows users to make purchases with a Near Field Communications Android phone and a compatible card reader. But: For now, at least, the service can only be used on Sprint's Nexus S 4G phone. Google says it "looks forward to bringing Google Wallet to more phones in the future". Supported Cards Besides Citi MasterCard and Google's Prepaid Card, Google will extend Wallet support to Visa, Discover, and American Express cards. Start Using Google Wallet If you've got a Nexus S 4G, you have to make sure you've updated Android to 2.3.7. You'll find out that Google Wallet comes loaded up as a native app. When you first access Google Wallet and link it to your Google account, you'll choose a four-digit PIN, which you'll enter each time you make a purchase. If your phone is stolen and the PIN is entered incorrectly five times, Google Wallet will be disabled. How this Works To actually use Google Wallet, you have to spy one of the three symbols at left. Then simply tap your phone against it and payment information is passed through the NFC chip. After payment is confirmed, your money will be transferred and a receipt will pop out. Data is encrypted on a "Secure Element" chip, which is is separate from the Android phone's memory. [youtube=http://www.youtube.com/watch?v=DsaJMhcLm_A] Photo: Google Blog