Sprint and Google announced the rollout of Google Wallet to all Nexus S 4G customers, an app that enables consumers to transform their phones into their wallets and make purchases by tapping their phones at the point of sale (POS).

Sprint is the first carrier and Nexus S 4G is the first phone in the United States to deliver Google’s solution. The new service currently only works with Citi MasterCard accounts and Google Prepaid MasterCard and is available at “hundreds of thousands of participating retailers, including American Eagle Outfitters, the Container Store, Macy’s, Foot Locker and Subway,” according to a press release.

Google Wallet requires users to set up a Google Wallet PIN that must be entered before making a purchase to prevent unauthorized access and payments.

“Shipping Google Wallet to Sprint is a crucial first step in creating a new way for people to use their phones to make shopping faster and easier,” said Osama Bedier, vice president of payments at Google, in the press release. “The world is on the brink of the next big shift in payments, and today’s announcement demonstrates that we’re making real progress in attaining the vision we share with our partners for a new and innovative mobile payments platform. We believe this is just the beginning of a transformation that’s soon to come.”

Eligible Sprint Nexus S 4G customers will be prompted to download the latest version of the Android software. Once this download is complete, customers can launch the Wallet app to try it.

Google said yesterday that it will add additional partners to its Mobile Wallet service in the near future. The company has received NFC specifications from Visa, Discover and American Express, meaning users will be able to add those cards to their mobile wallet soon.

Sprint has teamed with Google in deference of signing on with Verizon Wireless, AT&T and T-Mobile in the ISIS initiative, which also aims to enable NFC-based mobile payments. ISIS promises trials in limited markets by mid-2012.

Google unveiled its new social experience, Google+, an alternative to the now defunct Google Buzz. While Google+ clearly targets Facebook, it does so in a less structured manner and comes bearing a few gifts for the mobile user.

Google+ offers the ability for users to group contacts into social circles, allowing users to share relevant information with specific sets of people as opposed to sharing everything with everyone, as is the case with Facebook.

The new system adds some new ways for Google users to share on their mobiles as well.

“We didn’t want ‘just’ a mobile experience, however, so with Google+ we focused on things (like GPS, cameras, and messaging) to make your pocket computer even more personal,” wrote Vic Gundotra, senior vice president of engineering for Google, in a blog post.

Google+ puts a premium on location, allowing users to add location to every post if they so choose. The company also added an “Instant Upload” feature where users can automatically have Google upload pictures to a private album on Google’s cloud whenever they snap a new shot, which the company hopes will make sharing photos with friends on Google+ easier.

Google admits the new service may still have a few rough edges and is proceeding with a limited trial. Users can sign up here in hopes of getting an invite to the trial.

Google has launched in-app billing for Android apps, company executive Eric Chu announced in a blog post yesterday.

In-app billing will let Android users make purchases of digital goods like media files or upgrades for mobile games without exiting the app. The in-app billing service is handled by Google’s Android Market.

Several Android apps are already offering the service, including Tap Tap Revenge by Disney Mobile; Comics by ComiXology; Gun Bros, Deer Hunter Challenge HD and World Series of Poker Hold’em Legend by Glu Mobile; and Dungeon Defenders: FW Deluxe by Trendy Entertainment.

Niccolo de Masi, CEO of Glu Mobile, called the start of in-app purchases on Android Market a “very significant step forward.”

“The Android gaming market continues to demonstrate impressive growth and we are optimistic that over the medium term in-app payments on Android will generate revenue streams analogous to those on iOS,” de Masi said, referring to Apple’s rival operating system for the iPhone and iPad.

Apple launched in-app payments in 2009. Four of the 10 highest-grossing apps in the App Store – Tap Zoo, Smurfs’ Village, Zombie Farm and Texas Poker – are free but allow in-app purchases. The launch of in-app payments on Android could help developers make more money off apps for the competing operating system.

Apple’s in-app payments generated concern after children using their parent’s iPhones racked up huge bills buying digital goods through games like Smurfs’ Village. Apple has since changed how purchases within iOS games are authorized.