Adding to its rapidly growing suite of mobile applications and services, Google has applied for a patent for a mobile payments service that would allow users to make payments at retail shops using their mobile phones.

Using text messages, the system dubbed "GPay" would authenticate payments, debit the purchaser's account, and credit the seller's account.

Originally filed in February 2006, the application was made public by the U.S. Patent and Trademark Office last week.

Perceiving that future growth will come largely from advertising to mobile users, Google has launched an ambitious series of initiatives to accomplish in the mobile world what it has done in the online universe. The company has been making many of its popular online applications, including its leading search engine and its Google Maps and Gmail services, available on mobile phones over the last couple of years. Google has also signaled its intention to bid in the upcoming FCC auction of valuable wireless spectrum in the 700-MHz band, and in July it entered into a partnership with Sprint Nextel to provide users of the WiMax network the No. 3 U.S. carrier is building with Web services including e-mail, chat, and social networking tools.

Described as "a computer-implemented method of effectuating an electronic on-line payment," the system referred to in the patent application is similar to existing mobile-payment services, including the mobile version of PayPal. Such services have been available for some time but have had little success breaking through with merchants and with customers.

In June Verizon Wireless, the No. 2 U.S. carrier, said it would offer subscribers mobile-payment options through privately held Obopay. Verizon called the service "the first mobile payment offering for any major U.S. carrier." Three weeks later Obopay announced the closing of a third round of venture funding, worth $29 million.

Google already has an online payment system called Google Checkout, launched a year ago. In May it released the mobile version of Google Checkout, which works only for online purchases.

The difference between existing mobile payment systems and GPay (the term the application says would be used to initiating payment sessions via text message) is, of course, that GPay is backed by Google. In theory, Google could offer merchants a discount on (or elimination of) transaction processing fees in exchange for advertising purchases by the merchant -- making it a much more formidable competitor to other novel forms of payment being brought to market by large financial services companies such as Visa.

Still, the growing array of Google mobile initiatives doesn't have a cohesive centerpiece until the long-rumored mobile device with the Google brand -- already dubbed the GPhone and reportedly in development by Taiwanese handset manufacturer HTC -- makes its appearance.